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Sleep Cycles

Sarah-Louise Waters • January 18, 2021

(a.k.a. Why do I always wake up overnight?)

I was asked to write a blog post to explain why we often wake up overnight and what we can do to prevent it. In order to do so, it is first essential that I explain how we sleep. This blog is therefore about the theory of the human sleep cycle and my next post will focus more on how we can use this theoretical knowledge in more practical terms to our advantage.


Humans (like most animals) do not sleep in one solid block of sleep that is all the same. We sleep in a series of sleep cycles, passing in and out of different types (REM and non-REM) and different depths (stages 1-4) of sleep and wakefulness throughout the night.  


Sleep cycles change in terms of their length and constituents as we progress through the night and also as we age. For more information on the difference in sleep at various ages, please see my other blog posts on how sleep changes with age.


An adult sleep cycle during the first part of the night lasts for 90 minutes, with the majority of that time spent in deep non-REM sleep. However, as we progress through the night, our sleep cycles get shorter and shorter and the proportion of REM to NREM switches so that by the morning, our sleep is dominated by REM and the lighter stages of NREM sleep.


The sleep graph (hypnogram) above gives a simplistic outline of a young adult’s sleep throughout a night or an eight hour period. As you can see at the left hand side of the graph, we start off awake, drift quickly through sleep stages one to three and then spend approximately an hour in deep NREM sleep. Following this we come back up through the stages of sleep, hitting a short period of REM sleep at the end of the cycle before another cycle begins.


In the sleep cycles that follow, it takes us longer and longer to get in to and out of deep NREM sleep and we spend less and less time actually in this stage, with the last three or four cycles containing no deep sleep at all. You can also see that the total time taken to go through each cycle at this point is significantly reduced (around 45-55 minutes).


Our level of consciousness (awareness of being awake) and the likelihood of us being disturbed during sleep varies depending on which stage of sleep we are in at the time. The lighter the level of sleep (i.e. stages 1 and 2), the more likely we are to react to noise or a change in temperature etc in the room.


Probably the most controversial and interesting point to note on this graph is the small gap between the end of one sleep cycle and the start of the next when our brains return to being fully conscious or awake. There is less of a gap between our first and second cycles of the night but after this, the gaps can become much more noticeable. Therefore, the quicker the sleep cycles, the more frequent and apparent the gaps are between them and the more often the wakefulness. This explains why we are more likely to wake up and be aware of being awake in the early hours of the morning than during the first third of the night.


These periods of overnight wakefulness are entirely normal and all humans experience them. There does, however, appear to be a difference in how aware of them individuals are and, more importantly, how we respond to them.  


Some people do not appear to return to full consciousness and will not remember having woken up at all throughout an entire night. Others are very vigilant of the gaps between their sleep cycles and are able to tell you at exactly what time they woke up and how long they were awake. Most people move from one category to another and somewhere in between depending on health and lifestyle factors such as pain, stress levels, life events, hormones, exercise, and alcohol consumption etc and how safe/relaxed we feel in our physical environment.


In my next blog I will explore in more detail how the difference in attitude to nighttime wakefulness can set up a self-fulfilling prophecy and how we can avoid the short, natural gaps in our sleep cycles becoming long, drawn-out periods of anxiety and insomnia.


Additional Reading



Sleep cycles https://www.fromsoultosole.co.uk/sleep-cycles

Reducing overnight wakefulness https://www.fromsoultosole.co.uk/reducing-overnight-wakefulness

Sleep pressure https://www.fromsoultosole.co.uk/sleep-pressure

Circadian rhythm https://www.fromsoultosole.co.uk/circadian-rhythm

Causes of non-restorative sleep

By Sarah-Louise Waters • November 29, 2024
Why do I wake up still feeling tired? When we give ourselves ample opportunity to sleep and we don’t remember being awake overnight, it can be really frustrating to then wake up feeling as though we’ve not slept or at least that we’re not refreshed by that sleep. But why does that happen? This blog is all about the many reasons why we may not be getting restorative sleep.

How reading before bed improves sleep

By Sarah-Louise Waters • January 30, 2022
Reading is an amazing way of escaping from your own reality. When we become absorbed in a story that is not our own, whether that be via a book or a movie, we put aside our own moods, worries and emotions. The more empathic we are, the more we are able to put ourselves into the shoes of the characters and let go of our own personal narrative. The benefits of doing this before settling down to sleep, especially for us highly-sensitive empaths, are immense. The ease by which we can fall asleep, the depth of that sleep and its length are all governed by how "safe" our brains feel at the time. If we are stressed, currently going though an emotional or practical upheaval, or are generally finding it difficult to switch off from the day, then our brain is going to want to keep us awake in order to continue its processing. Annoying as it is, this is simply your subconscious' way of sifting through data, resolving problems and (hopefully!) finding solutions. While nothing will ever truly be a better option than dealing with whatever is stressing you out in daylight hours, it would be ridiculous to think that there will never be a time that you go to bed with something on your mind, and this is especially true for highly sensitive, empathic individuals. Reading a book (even for a short space of time) can offer you the distraction that you need to put this issue to one-side and drift off. There are however some rules to remember when it comes to pre-sleep reading, particularly with regards to the content of what you read... 1) The topic should be interesting enough to capture your attention and stop you thinking about your worries. A text book may work, but only if you can actually concentrate on what you are reading without your brain wandering off on a tangent. 2) Reading about something you find emotionally disturbing (murder, rape, child abuse etc) will raise your blood pressure and heart rate, both of which are detrimental to sleeping well. 3) Reading a thrilling page-turner may lead you to still being awake at 2am because you just want to finish the next chapter, and the next, and the next (you get the idea!). 4) Picking a favourite book that you've already read can be a great idea - it will give you all the feels and distraction, without the need to continually page-turn as you already know what's coming. 5) If you find reading difficult because you are sight-impaired, dyslexic or have another form of reading difficulty, or simply because reading reminds you of an academic past you would rather forget, listen to an audiobook instead. You're still getting all of the sleep advantages of reading, but without the discomfort. 6) Never read anything related to your work just before bed. Reading should be about distancing yourself from stress, not inviting it in. 7) Be aware that reading on an electronic device means subjecting yourself to additional cues that now is not the right time for sleep (i.e. blue light exposure). Kindles don't smell or feel as good as a proper book either! If you are finding it difficult to fall asleep and would like some further help in the form of some sleep coaching sessions, please click on the button below and I will get back to you as soon as possible. 
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