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Sleep is fundamental to our health and wellbeing. In Sleep Sense, international sleep expert Dr Katharina Lederle explores sleep's connection to each of the three pillars of successful living: physical health, cognitive performance, and emotional wellbeing, and provides readers with the tools to effectively establish healthy sleep habits.
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Seitenzahl: 263
Veröffentlichungsjahr: 2021
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SLEEP SENSE
IMPROVE YOUR SLEEP,IMPROVE YOUR HEALTH
DR KATHARINA LEDERLE
Dr Katharina Lederle is a human sleep and body clock specialist who helps people improve their sleep and live their lives to the full. She is also founder of Somnia, a boutique sleep science and therapy organization. Katharina gained an MSc in Biosciences at Ruprecht-Karls University, Germany. She then completed a PhD in Human Circadian Physiology and Behaviour (the human body clock) at the University of Surrey, UK. Her PhD looked at the effects of light on human sleep patterns, specifically in the elderly. Katharina is also trained in Mindfulness, Acceptance and Commitment Therapy and Compassion Focused Therapy, which she uses in her work with insomnia clients. Based in London, she has worked with a number of sleep-centred organizations, including Clockwork Research where she advised national and international airlines, emergency helicopter services, petrochemical and mining companies around the world on sleep and fatigue. She also provides sleep consultancy services to a range of businesses and institutions, including management consultancies, universities, other sleep therapy providers and pharmaceutical companies. Through Somnia, Katharina raises awareness about the importance of healthy sleep and provides one-to-one sessions, sleep workshops and educational talks on helping people sleep well and feel good. Katharina can be contacted at [email protected]
PRAISE FOR SLEEP SENSE
‘A book that is a pleasure to read! Clearly stated and engagingly written, Katharina Lederle draws on her research expertise and work experience to explain the latest scientific knowledge about sleep and why good sleep matters so much to our health and wellbeing. Her inviting practical approach to making sleep a priority is easy to implement in daily life — it combines science with an understanding of the reader’s everyday life. A recommended read!’
— Professor Debra J. Skene, Sleep and Circadian Rhythms Researcher
‘This is a very fluid read, it describes all facets of sleep in deep detail that anyone can understand. Every sleep condition is covered and it serves as a very good guide of how to improve your sleep for any reader. I found the hints throughout to be particularly useful. After reading it I realized I have bad sleep habits, and understanding the long-term effects (not
evident in the short term) has made me change my habits, by prioritizing my sleep.’
— Dr Justin Hamilton, Subsea Controls Engineer at BP
‘I enjoyed reading both the science behind sleep alongside the practical examples everyone can relate to. I get up for an early commute every day just before 5 a.m., and hence my average sleep duration is only about 6 hours. This book has made me challenge myself rather harder as to how I can change my work/life balance somewhat to get my average weekly sleep duration closer to 7 hours (the minimum recommendation). An interesting read!’
— Will Jones, Vice President Business Operations at Fiserv FINkit
‘Nothing could be more fundamental to our healthy functioning and wellbeing than sleep, and yet it can often be a focus for worry. When rest eludes us, we can over-analyze, over-medicate, and over-complicate in our search for a solution. In a straightforward, easily accessible style, Sleep Sense informs us about the simple building blocks of healthy sleep, and teaches us to work with, rather than against, our natural and
individual sleep patterns. Her expertise makes Dr Lederle a perfect coach to help us implement the behavioural changes necessary to achieve not just better sleep, but a healthier life.’
— Dr Elaine Kasket, HCPC-Registered Counselling Psychologist
‘A very helpful, practical and balanced perspective on sleep — encouraging us to look at sleep as a mindful activity to be prioritized, but also to feel relaxed about it, accepting occasional changes in sleep experience as normal rather than worrying about sticking to a rigid pattern.’
— David Champeaux, Director, Global Cognitive Health Solutions at IPsoft
PRAISE FOR DR LEDERLE
‘Dr Kat has been an invaluable source of advice on sleep and the problems that we can all encounter when life takes an unexpected turn. But just as importantly, her patient and gentle approach soothes like a warm blanket in times of need.’
— Dr Stuart Greig
‘I found Dr Kat incredibly helpful. Her expertise is reassuring in addition to which she’s a great listener, so I came away feeling I’d been heard and had a programme designed to meet my particular needs. I was particularly impressed by how generous she was in replying to my emails asking for further advice and reassurance, which she was always ready to give.’
— Mark Wakefield
‘After a lifetime of poor sleep, I bless the day I had my first consultation with Dr Kat. She was so supportive and encouraging — she always understood what I needed and my sleep is now improving. I never thought I’d be able to sleep well again. She has taught me so much and I will be forever in her debt.’
— Valerie
‘My students were fascinated by Dr Lederle’s guest sessions, the far- reaching influence that sleep has on our lives was expertly presented, and the breadth and depth of Dr Lederle’s knowledge is very impressive.’
— Nigel Brown, Lecturer
To my parents and Alexander
CONTENTS
Welcome
Introduction
Part 1: A short tour of sleep
1. Sleep: the most frequent questions answered
2. Light and sleep
3. Sleep in women
4. Dreaming
Part 2: Why healthy sleep matters
5. Sleep and physical health
6. Sleep well to perform well
7. Emotional wellbeing and sleep
Part 3: When sleep goes wrong
8. Sleep-related breathing and movement disorders
9. Chronic insomnia disorder
10. Hypersomnias
11. Parasomnias
12. Circadian rhythm sleep–wake disorder
Part 4: Weaving healthy sleep habits into your life
13. A scaffolding for healthy sleep
14. Dealing with sleep issues
Parting words
Glossary
Acknowledgments
References
Further reading
Index
WELCOME
I’m Katharina Lederle. My clients call me Dr Kat. My dad calls me Ninchen (which means ‘little Katharina’), but he’s my dad so he’s allowed! That aside, I’m what people refer to as a sleep specialist, therapist and educator. In other words, I help people improve their sleep and ultimately their wellbeing. The short answer to why I wrote this book on sleep, and who for, is that I want to raise awareness of sleep and how vital it is for a healthy life. By doing so I hope to have a positive impact on the lives of as many people as possible — many more than I can reach through educational talks or one-to-one sleep therapy sessions.
There are three things I want you to take away from this reading this book. First, occasionally sleeping a little less or a little more, going to bed a little earlier or a little later than what’s normal for you is just that: normal. Second, your lifestyle and behaviour can have a huge impact on the quality and quantity of your sleep. If you experience sleep problems regularly or often shift your sleep timings, then that can have negative consequences for your sleep and your quality of life. Third, by making sleep a priority — and that doesn’t mean you must follow a strict routine every day — you keep your sleep healthy and yourself healthy. That in turn will benefit your family and friends, because a healthier you is a happier you.
What’s not to love!
INTRODUCTION
I’ve written this book to help you understand what sleep is and why it matters. It will help you gain a better understanding of the importance of sleep and the fundamental role sleep plays in your everyday life. It will help you recognize when your sleep has gone a little off-track, and will also help you get to the heart of why this might be, to take the right actions, make positive changes to sleep better and feel good as a result.
If you’re a person with a busy lifestyle — maybe a working mum or dad or a busy professional — you’ll learn more about how sleep affects your physical health, cognitive performance and emotional wellbeing. It will help you optimize your sleep in a way that helps boost your performance and productivity.
The sleep habits and hints this book contains give you simple and easy-to-apply insights about how to maintain a healthy, happy emotionally balanced life — naturally.
To make the content of this book as relevant as possible, I asked my family (including my dad — he’s a farmer so he gets up early!) what their burning questions on sleep were. Some of what they came back with is answered in Chapter 1. Other questions from them, as well as from my clients, informed entire chapters such as those on sleep and health and wellbeing. One of the most frequent questions I get asked is, ‘What can I do to improve my sleep?’ To some extent this depends on why you don’t sleep enough, so a quick answer is rarely efficient. I’ve included ‘Part 4: Weaving healthy sleep habits into your life’ where I’ll discuss different strategies. Ultimately, it’s about developing and implementing healthy sleep habits for yourself. But to give you the one overriding strategy right here at the start of the book: make sleep a priority in your life.
Where possible, I’ve included examples from friends and family members who occasionally experience poor nights. Their stories will tell you what they experienced during the evening and night, how they tried to remedy the situation and what impact that had. My hope in sharing these personal stories is twofold: firstly, that you’ll find the stories engaging and that they’ll resonate with you, and secondly, that through them you’ll be able to learn to quickly identify why you struggle with sleeping soundly, what skills would be most helpful in particular situations, or what you can do to minimize the occurrences of poor nights.
Did you notice that I said ‘minimize’ rather than ‘prevent’ poor nights? That’s because poor nights are part of normal sleep. Sleep isn’t an absolute constant. Just as you might occasionally have a bigger or smaller appetite, or get ill with a cold for a week, you might occasionally sleep a little less or a little more than what’s normal for you. Sometimes you might be able to identify a particular reason, while at other times you can’t. The point is that this is part of normal life, and you don’t have to worry or get stressed about not sleeping ‘properly’ for a few nights. When your sleep is back on track, aim to get the recommended seven to nine hours, or whatever your personal sleep need is. The healthier your sleep, the more easily you can deal with sleep outliers.
There’s a difference between an occasional poor night and regularly sleeping too little, though. In the next part of the introduction I’ll highlight some findings from a recent international sleep survey that compared how long people said they slept with how much sleep they said they needed to function optimally. Not surprisingly, there was quite a gap between the two.
At the end of each chapter I’ll give you a little summary to highlight the key points, along with suitable helpful hints throughout. It’s the last section, Part 4, that I really hope will show you ways to make sleep a priority.
This book is for healthy sleepers, for people with an interest in sleep and those who want to learn more to optimize their sleep. An occasional poor night is part of normal sleep, part of normal life. This book is not intended as a resource for those with an ongoing or repeatedly occurring sleep problem. If your sleep problems persist and start to affect your daily life and wellbeing, or if you suffer from chronic insomnia, please see your GP or sleep specialist and get checked for sleep disorders or other medical conditions. However, following healthy sleep habits as outlined in this book will assist any treatment plan.
SETTING THE SCENE
You will have heard that sleeping too little has become a health epidemic in the western world. Sleep is vital for each of the three pillars of health and wellbeing: your physical health, your cognitive performance and your emotional wellbeing. It underpins all three of them. If we don’t get the amount or quality of sleep we need, we run the risk of physical and mental illness. Sleep health matters.
There’s a plethora of reasons we might not sleep enough, and I’ll leave that discussion for the last chapter where we look at healthy sleep habits. For now, I want to share some of the findings from an international sleep survey of six western countries including the United Kingdom, the United States and Germany, to provide you with some insight into the extent of this new health epidemic. (For the entire survey report, please see p. 208.)
For the three countries mentioned, over 50 per cent of people said they get half an hour less sleep each night than they need. That adds up to quite a bit over the course of a week. Just over 40 per cent of people said that they get a good night’s sleep every night; yet more than 50 per cent felt that inadequate sleep affects their mood and performance. So, if sleep is so important to how we feel and function, why aren’t we making good sleep a priority?
Finally, when asked how often they looked online for information relating to sleep, over 60 per cent of respondents from the United Kingdom and Germany said they didn’t look online for sleep-related information. Nearly 70 per cent of respondents from the United States did search online, but they did so rather infrequently, less than every three weeks. Sleep health matters.
This brings me back to the purpose of writing this book: to raise awareness about sleep and provide sleep education to a wider audience. I want to ignite some fascination with sleep as a topic and an activity! And I hope that reading this old-school book can help you to find ways to optimize and maintain healthy, normal sleep.
Enjoy the read,Katharina
PART 1
A SHORT TOUR
OF SLEEP
Sleep is the most exquisite invention.
— HEINRICH HEINE, 1856
1.
SLEEP: THE MOST FREQUENT QUESTIONS ANSWERED
When people hear I’m a sleep specialist, they ask me all sorts of questions about sleep: what is its role and function, what regulates it and how much sleep do we need? The best way to address these questions is to give you an understanding of what normal sleep is.
I’m going to take you on a sleep tour. Along the way we’ll stop off at some of the most interesting questions people ask, to give you a good overview of the topic. I’ll talk about what sleep is and how it comes about. I’ll explain what happens in your brain when you sleep. And why, for example, you feel sleepy after lunch. I hope to surprise you with some interesting facts and amuse you with some theories on what might help you sleep better. But, above all, I hope that reading this chapter will interest you enough to want to learn more about sleep, because I see this short sleep tour as the introduction to sleep on which all the other chapters of the book build. To get the most from this book, read this chapter first and stay on the guided tour — that way you won’t miss anything.
WHAT IS SLEEP AND WHY DO WE DO IT?
Sleep is a naturally occurring state that alternates with being awake. Typically, we spend one-third of the 24-hour day asleep and two-thirds awake, fully conscious of what’s going on around us. Sleep is a shift in consciousness. It’s a time when we ‘switch off’ from the world around us and become less responsive to it. However, that doesn’t mean our brain and body are doing nothing while we sleep.
During sleep many diverse physiological changes take place. The purpose of sleep isn’t yet fully understood; it has been hypothesized that, among other things, sleep allows both our brain and body to replenish and restore, as well as consolidating memory and strengthening the immune system. Lack of sleep, by contrast, has detrimental effects on many areas such as our physical health, cognitive abilities like memory and alertness, and emotional wellbeing.
According to the Sleep Homeostasis Hypothesis (SHY), sleep’s core function is to enable learning. SHY states that while we are awake and ‘experience’ things our brain cells form new connections with each other (this is called brain plasticity). Because of the skull there is a natural limit to these connections. However, during sleep when the brain is ‘offline’, some connections are cut back, allowing space for new learning to take place the next day. Clearly, many questions remain; how it is decided which connections to keep and which to cut back, for example. Luckily, researchers are working on this!
WHAT MAKES SLEEP HAPPEN?
Sleep happens when specific areas of our brain simultaneously activate and deactivate. Depending on which area is activated, either wakefulness or sleep will be promoted.
The arousal system is responsible for keeping us awake. This system is located within the brain and consists of certain parts of the hypothalamus, basal forebrain and brainstem. The sleep-promoting system also sits in the hypothalamus, which is involved in controlling many physiological factors and functions in your body. Using specific neurotransmitters (messenger molecules in the brain) and a mechanism not dissimilar to an electronic on–off switch (for which the scientific term is ‘flip-flop switch’), both systems inhibit one another. So if, for example, the arousal system is active it suppresses the sleep-promoting system. That’s what makes sleep and wakefulness mutually exclusive: you’re either asleep or awake, and the switch between the two states is normally rapid and complete. However, a malfunctioning switch — where the transitions are no longer swift and wakefulness spills over into sleep or vice versa — can be a cause for sleep disorders.
Neurotransmitters are used by the brain for cell-to-cell communication. Their interactions link different brain areas to form networks, which they then either activate or deactivate. Important excitatory neurotransmitters used by the arousal system include acetylcholine, orexin, serotonin and histamine (which explains why antihistamine tablets can make you drowsy), while those used by the sleep-promoting group include GABA and galanin.
Histamine, for example, makes you more alert, helps you to think more clearly and gets you motivated. GABA is the brain’s major inhibiting neurotransmitter. It basically blocks the effects of the excitatory neurotransmitters. So, sleep is of the brain and by the brain. But sleep isn’t just crucial for brain functioning; it’s also necessary for our body and mind to function optimally.
HOW IS SLEEP REGULATED?
Many of us see sleep and falling asleep like flipping a light switch: if I do this and don’t do that, I’ll sleep. But it’s not that straightforward. The cycle of being asleep and being awake is complex and involves several brain areas and signalling systems. Fundamentally, it’s the interaction of two somewhat opposing processes that regulates these brain regions and signals, and that regulates our sleep–wake behaviour.
One process monitors time awake and is responsible for the pressure we feel to sleep. We call this the sleep drive or sleep pressure. The second process is called the circadian pacemaker or internal body clock. This generates signals for sleep timing. It may appear a little complicated but a slow walk through the processes and a diagram can help. Take a look at Figure 1 and then let’s find out what each of the two processes actually are.
The sleep drive
The sleep drive, or the need to sleep (the thin black line in Figure 1), is affected by how long you have been awake: the longer this is, the greater the pressure to sleep. The sleep drive is often likened to an hourglass, where sand flows from one side to the other (from wakefulness to sleep), and when it is full it is flipped over and the sand flows back (from sleep to wakefulness).
To explain it in detail, the longer we’re awake, the more adenosine (a nucleoside) accumulates in our brain. Adenosine is a by-product of the brain’s metabolic processes and is seen as a biomarker of sleepiness because it binds specific groups of cells in the brain, slowing down their activity, which makes us feel tired. The more adenosine that is bound, the greater the increase in the drive to sleep. Once levels of bound adenosine hit a certain threshold — i.e. once one side of the hourglass is full — the likelihood of falling asleep is high. That’s when we feel really tired and generally go to bed and sleep. While we’re asleep, adenosine disconnects and the drive to sleep dissipates — the hourglass sand flows in the opposite direction.
Figure 1: The interaction of the sleep and circadian drives
In typical sleepers it takes about sixteen hours for adenosine levels to reach the necessary threshold, followed by an eight-hour sleep duration. But it only takes a few hours for the drive to sleep to dissipate. So if we were to wake up at this point, after approximately four hours’ sleep, we would have slept too little and this would have detrimental effects on our wellbeing and performance. Luckily the second mechanism, the circadian pacemaker, comes into play at this point.
The circadian pacemaker
The internal circadian clock (from the Latin circa meaning around, and dies meaning day) or internal body clock acts as our body’s timekeeping system. It’s responsible for setting the rhythm (timing and duration) of our behavioural, psychological and physiological functions and processes, one of them being the rhythm of sleep and wakefulness.
The circadian clock comprises a specific group of neurons called the suprachiasmatic nuclei (SCN), which sit in yet another area of the hypothalamus. I like to compare the SCN to the conductor of an orchestra, setting the rhythm for the rest of the body. This is important because each organ, and in fact most of our cells, has its own clock and would function according to its own rhythm if it wasn’t for the internal clock. Just as every musician in an orchestra has his or her own rhythm, without a conductor they soon would play out of time. For our bodies, the equivalent is that all our behavioural, physiological and psychological processes would be misaligned with one another as well as with the external day. We simply wouldn’t be able to function in a way appropriate to the time of day if it wasn’t for the master clock and its synchronizing abilities.
The internal clock has its own rhythm, which is slightly longer than the external 24-hour light/dark cycle; on average, it’s around 24 hours and eleven minutes. Over time this means our internal clock will start to lag behind the external day. When this happens, our individual activities and biological processes will be mistimed or get out of sync with the external day. As a result, we exhibit the ‘wrong’ behaviour for a given time of day and this can have the effect of reducing our chances of good health — and survival.
To better illustrate my point, here’s a short metaphor. Let’s go back in human evolution and imagine it’s several thousand years ago. You sleep during the day and you’re awake at night, which is when you leave the safety of your cave to go hunting. Unfortunately, your night vision isn’t great, so you don’t notice the lioness until your head is in her mouth … her night vision is far superior to yours.
Obviously, this isn’t an ideal state to be in. To prevent this from occurring, the clock needs to be synchronized by environmental time cues (known as zeitgeber, German for ‘time giver’) on a daily basis to be aligned with the solar 24-hour day. The 24-hour light/dark cycle is the strongest of these time cues; ‘lights on’ signals daytime and ‘lights off ’ signals night-time to the clock. Your internal clock then relays this information via the hormone melatonin to the rest of your body. (In Chapter 2 I’ll come back to this and explain how light impacts your internal clock and how it regulates the production of melatonin.)
The key point here is that your internal clock regulates when to sleep — and when not to sleep — during the 24-hour day. It maintains a separation of wakefulness and sleep, dividing them into different episodes with one during the day and the other at night, and perhaps a short one in the afternoon.
How does this help us to stay asleep?
How do the need to sleep and the internal clock interact?
In the early morning hours, when the sleep drive has dissipated and the ‘sleep’ side of the hourglass is empty, arousal from sleep becomes much more likely. At the same time, the circadian clock sends out a sleep-promoting signal to consolidate our sleep and prevent us from waking up too early. Once this signal ends, we wake up and the ‘sleep’ side of the hourglass starts to fill up again over the course of the day.
IS THERE SUCH A THING AS DEEP SLEEP?
Yes, there is. And there are even a number of other sleep stages, too. First of all, the brain shows distinct waves during wakefulness and sleep. Using polysomnography, where electrodes are attached to your head, researchers can record brain waves.
Sleep itself can further be divided into two broad states: rapid eye movement sleep (REM), characterized by fast, wake-like waves, and a quieter, non-rapid eye movement sleep (NREM). The repetition of alternate NREM and REM stages results in sleep cycles, each with a duration of 90 to 120 minutes. For the typical sleeper, this equates to four or five cycles per night. The graphical representation of this sleep-stage cycling is called a hypnogram — it’s the line that goes down and up in Figure 2 (I’m a great fan of visualizing things during a discussion). When I explain a hypnogram I often compare sleep to a symphony and the hypnogram to the score.
The squiggly lines on the left are the brain waves for each sleep stage. NREM sleep can be subdivided into three stages, each reflecting a different depth of sleep.
NREM stage 1
We enter sleep via NREM stage 1 (N1). This is a very light sleep: you become drowsy, your eyes move slowly and your muscles start to relax. Your brain waves also start to slow down and their oscillations become bigger — we call them theta waves. This is a transitional phase from wakefulness to sleep, when you’re neither fully here nor there, you’re simply gently drifting off to sleep. For example, if your partner says your name while you’re in this phase you’re likely to respond, and you can still detect certain types of smells. You may also experience sudden twitches or muscle spasms, called hypnic myoclonic or hypnic jerks. These are nothing to worry about. They’re just an involuntary twitch of a muscle — hypnic is short for hypnagogic, meaning that it’s happening during the transition from wake to sleep.
Figure 2: The hypnogram
You can also experience jerks at the transition from sleep to waking; these are called hypnopompic jerks. You might sense a feeling of falling or weightlessness and experience hallucinations or visual imagery at this point.
Since N1 is a lighter stage of sleep we can often misperceive such sleeping for being awake. For those lucky enough to have a bedfellow, have you ever turned to your partner to say, ‘I didn’t sleep last night’ only to have your partner look at you and say, ‘Yes, you did’? It may have been that during the night your sleep was disturbed and you spent more time in N1 than usual, and you interpreted your feeling of unrefreshed sleep as a lack of sleep altogether. However, if such feelings occur regularly then it’s important to see a sleep specialist to check for any potential sleep disorder, such as insomnia.
NREM stage 2
NREM stage 2 (N2) sleep is also a light phase of sleep, though one during which everything’s taken down a notch. It becomes more difficult to be woken up from N2 compared to N1. In addition to more theta waves, we see rapid brain wave features called sleep spindles and K-complexes appear. Both patterns play an important role in memory formation and learning. And on a physiological level, we observe a decrease in body temperature and a slowing down of breathing and heart rate.
Fascinating new studies have shown that, while in N2, the brain is still able to respond to external stimuli and perceptual learning occurs.
NREM stage 3
NREM stage 3 (N3) is what is called slow wave sleep (SWS) or ‘deep sleep’. The dominating brain waves we see now are slow, big delta waves, and the amount of SWS correlates to our sleep drive or pressure, meaning that the higher the pressure (for example, because we have gone to bed later than the usual time), the more SWS will occur during the following sleep period. It takes some effort to wake someone up out of deep sleep; breathing, heart rate and blood pressure slow down even more and the body temperature drops further. The muscles are even more relaxed, but are still active. N3 is the phase of restoration and it helps the consolidation of fact-based memories such as learning new vocabulary for your German class or events you have experienced that day, for example. (By the way, sleep spindles occur during N3, too.)
REM sleep
Finally, we come to REM sleep, which gets its name from rapid, rolling eye movements. In fact, your eye muscles are the only muscles you can use during this stage. The rest of your body is almost paralyzed. There might be some occasional twitches in the peripheral muscles, but for most muscle groups we experience atonia to protect ourselves from acting out the often vivid dreams that can happen during REM sleep. (Incidentally, we also dream in NREM, but our dreams are more thought-like, less vivid and less well remembered than those during REM sleep.)
During REM sleep, breathing rate, blood pressure and heart rate are elevated compared to NREM — in fact, they’re more like those of someone who’s awake. If you look closely at Figure 2 you might notice that the pattern of the brain waves during REM sleep is a very active one and looks very similar to being awake. That’s why this stage is also called ‘paradoxical sleep’. REM sleep is often linked to the consolidation of motor and perceptual skills (it’s about how to do something, like riding a bike, for example) but also emotional memories, since brain regions involved in emotional processing such as the amygdala and hippocampus show an increased activity during REM sleep.
Similarly to N2, the brain remains responsive to external stimuli (e.g. noise, your own name) and is able to learn during REM sleep.
So, to summarize, a healthy sleeper …
• enters sleep through N1
• has several (four to six) sleep cycles
• has more NREM sleep in the first third of the night
• has more REM sleep in the last third of the night
• spends around 75 per cent of sleep time in NREM (divided broadly as follows: N1 about 5 per cent of total sleep time, N2 about 50 per cent and N3 about 20 per cent)
• spends around 25 per cent of total sleep time in REM.
It’s also worth noting that wakefulness during the night is part of healthy sleep behaviour (5 per cent), which we’ll come to in a moment.
Are certain sleep stages more critical for our health and wellbeing than others? No, not at all. While the different sleep stages enable different processes, none is more important than the others.
