Dr. Jason Ellis is a Professor of Sleep Science and Director of the Northumbria Sleep Research Laboratory in the United Kingdom. He is a qualified Somnologist – expert in Behavioural Sleep Medicine, a Practising Health Psychologist, and author of The Insomnia Cure. (Our conversation has been condensed and edited for clarity.) 

What is the function of sleep, and what happens in the brain and body when we sleep? 

Sleep medicine is actually quite a young topic, only about 70 years old. Sleeping may seem like a passive activity – you’re quiet and still, with your eyes closed, breathing is slow and rhythmic. It was only in the 1950s, that we started to understand that there is in fact, a lot more going on than that. Sleep really is a reflection of daytime activity where you are walking, talking, and using up lots of energy. At nighttime, you use about the same amount of energy, but it’s diverted internally. 

There are two main stages of sleep. Firstly let’s talk about REM or rapid eye movement sleep. When we look at people’s brains during this stage, it tends to look almost like they’re awake. It is during this phase that dreaming, long-term memory consolidation and emotional regulation occur. For example, if you’ve had a bad day, if you’re stressed, or you’ve seen something traumatic, it’s during REM sleep that your brain attempts to organise, work through and make sense of those experiences. 

The other main stage is called non-REM. Taking up 75% of the night, non-REM sleep is made up of four semi-distinct stages. Stage 1 is where your brain activity starts to slow down and should only take about 5-10 minutes. Stage two takes about 50% of your whole night and in effect, acts as a filing system where your brain decides what is important to remember (which is consequently turned into long-term memory) and what is less important (which is, therefore, forgotten). It also acts as a way to protect deep sleep and REM in the face of noise or pain. 

Finally, we’ve got stages three and four. This is a period of deep sleep in which restoration and repair occur. The main area of focus here is the endocrine system, which uses hormones to regulate your body’s vital internal processes such as energy availability, reproduction, stress management, growth and development. Immune system functioning is also closely tied to deep sleep. More recently, it was discovered that certain toxins, such as beta-amyloid (a protein associated with Alzheimer’s disease) are removed from the brain during deep sleep. 

So in essence, if we don’t get a sufficient amount of sleep, and certainly enough deep and REM sleep, it can have a detrimental impact on our physical health, mental and emotional health, both in the short and long term.

What is the optimum amount of sleep that we should get? 

Every individual has different sleep requirements, since we are all unique beings all leading drastically different lives. While there is no definitive number, there is a general optimal range for adults which is around seven to nine hours per night, plus or minus an hour. 

Below six or above ten hours tends to be a sign of an abnormal sleeping pattern in many people. But really, the key point is how do you feel in the morning? About half an hour after you’ve woken up, ask yourself, “How do I feel? Do I feel tired? Do I feel exhausted? Do I feel like I could go back to bed?”. If the answer is yes, then that is a sign that there is an issue with the quality, the quantity or the timing of somebody’s sleep. 

How can you measure sleep quality? 

If you are alert throughout the day, the time it takes for you to fall asleep is not too long, and if your sleep is unbroken, this generally indicates you are experiencing good quality sleep. The periods of sleep should take place somewhere between 9pm and 8am, and the duration of sleep should last between six and nine hours. 

Can you measure sleep quality by measuring brain activity? 

We’ve talked about sleep stages, where stage one is falling asleep, stage two is light sleep and stages three and four are a deep form of restorative rest. Throughout the night, you progress through stages one to four and then you enter REM sleep. This is known as your sleep cycle and each iteration should take 90-100 minutes before it repeats itself. Over the course of the night, you’ll get most of the slow wave deep sleep in the first half of the night. In the second part of the night, you get a lot more REM sleep, and this makes sense from a biological perspective. It is important to keep the human body alive and efficient and working, and that’s why we capitalise on those early hours, to get much more slow wave, deep sleep. In the latter part of the night, we’ll deal with emotions and memory. Each sleep stage exhibits different brain wave activity and so, measuring how much of each of those stages people are getting would provide a good insight into sleep quality. But of course, it’s very difficult to measure this outside of the laboratory. Therefore, we have to rely on how people actually feel about their sleep. 

What is insomnia and how is it diagnosed? 

Insomnia is the most common sleep disorder affecting about 10-15% of people in a population. There is a diagnostic classification system for insomnia which relies on the responses to several questions, for which there is no known biological origin. We would generally classify insomnia as being dissatisfied with your sleep, including difficulties of getting to sleep or staying asleep, or waking up too early in the morning. Naturally, if you don’t give yourself enough time for sleep,

then you’re going to be in a sleep deficit. However, the problem arises when the individual experiences notable daytime dysfunction or impairment. What we mean by that is, it’s more difficult to work, to manage the household, to maintain interpersonal relationships, or one might experience difficulties with mood stability, memory, or concentration. These issues should persist for at least three months to get a clinical diagnosis. 

The work that I do is looking at the early stages of this condition, with a view that we can prevent the onset of insomnia. Thus far, what we’ve understood is that having two weeks of sleep problems, usually in response to stress or anxiety, is normal. Any longer is abnormal. You can’t elicit a stress response for very long without starting to damage the body itself. After the two week mark, they should be treated as quickly as possible in order for the intervention to have the most efficacy and chance of success. 

Do you have any advice for people who struggle with sleep and who could be in the early stages of insomnia? 

Issues within a two week period, as we’ve said, can be quite a normal adaptive response to stress. However, the most important thing to do during this period is to do nothing. There will be a tendency to want to compensate for the lack of sleep which may, at the moment, appear logical, but these things can actually turn it into a long term problem. Strategies such as drinking more coffee to stay awake, drinking alcohol to get to sleep, lying in a little later, or having a nap are all in fact, detrimental to the sleep cycle itself. If you avoid these strategies in those first two weeks, your body will correct itself and normal sleep should resume. 

If these sleep issues persist, there are a number of alternative interventions that may help manage the problem. For example, if you are in bed and struggling to get to sleep, get out of bed. By lying there awake for a long time, we are likely to get angry, frustrated, and worried. And it’s these negative emotions which we then start to associate with the bedroom itself. This mindset is not particularly compatible with sleep, and even as normal sleepers, trying to rest following an argument with a partner, for example, is extremely difficult. In this instance, get out of bed, go and do something relaxing for half an hour. It is important to actually get out of bed and leave the room, if practical, to avoid introducing lots of daytime behaviours into your desired sleep space. Otherwise, this blurs the line between where you associate areas of wakefulness and sleep. 

Beyond the three month mark, that’s when we might want to consider therapy. Cognitive behavioural therapy for insomnia is very effective and works for about 60-70% of patients lasting for at least 10 years. The only reason we don’t know it lasts longer at this point is because we haven’t studied it for more than 10 years yet.


  • Nicole is Head of Practitioners at Walking on Earth, a digital holistic health platform. She has a bachelor's degree in Psychology and Neuroscience from Maastricht University and a masters degree from VU Amsterdam. She is passionate about using technology to help people make their lives better so they can spend more time doing what they love. Walking on Earth satisfies that interest by providing a platform that helps people learn the tools and techniques to build resilience and live happier and healthier lives.