Why am I tired all the time? The science of sleep

Naps, alarms, sleeping pills, sheep: Dr Nick Knight describes why we need sleep, how much is enough, and how to make the most of it
  • @Dr_NickKnight

“I never had this problem on that date last week”, I yawn pitifully to myself as the whites of my eyes pierce the darkness, their only companion the illumination of my mobile-phone screen as yet another message comes through.

Like many, last night, I really struggled to fall asleep. Sleep is a bit like queuing in England - we don’t know why we have it but wow, we really can’t do without it. With modern life packed with increasing and competing pressures from work, family, and social change, many of us, about a third of the UK population in fact, face the prospect of six hours sleep per night or less, according to a study by The Sleep Council.  As a result, we exist in an era in which the modern populace experiences excessive daytime sleepiness and fatigue secondary to this chronic sleep loss.

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Sleep can be defined as that reversible behavioural state in which you are perceptually disengaged from, and unresponsive to your environment. The reversible part is important, for without that, you are in a coma.

You can divide your sleep into four stages. The first three stages are called non-rapid eye movement (non-REM) in which you fall into a progressively deeper sleep with increasingly less reaction to environmental stimuli (like your fidgety partner). The final stage, called rapid-eye movement (REM) sleep, is where you are essentially an active brain in a paralysed body - and it is here that you dream. Now you cycle through all four stages about every 90 minutes (with 25% of your time being spent in REM sleep) and so overnight you will experience roughly 5 to 7 sleep cycles. I know, I know – it’s never enough.


Of course the question is, why do we sleep? After all, there are no known animals (including us) that live without sleep – so it must be needed. Frustratingly however, the honest and remarkable answer is that we don’t know what the key function of your sleep is. Generally, however, it is (and I am sure you would agree) accepted to function in order to permit recovery from previous wakefulness and prepare you for functioning in the subsequent wake period (though, yes, admittedly, sometimes that doesn’t quite work out as we had hoped).

It is too appreciated that there are very important biological functions to sleep, which include supporting your body’s physiological processes, memory processing and learning.

Of course modern living, whether a result of work or play, occasionally lends itself to a sleepless night or two. In fact, The Sleep Council say that almost half of Britons say that stress or worry keeps them awake at night. The result is that you become sleep deprived. If you then continue this pattern of ‘partial sleep reduction behaviour’ you would slowly accrue a sleep ‘debt’; this is a bit like over-spending on your credit card – you will need to pay back before you can function properly.

Now, I am sure that you would have experienced the fury of 'sleep debt' at some point – you know, that feeling as your body becomes uncontrollably engulfed with that increased drive to sleep, decrease in daytime alertness, and fall in physical and mental performance. Sleep deprivation negatively impacts upon a plethora of your psychomotor performance – accuracy, reaction times, decision-making, errors rate, and mood. After a run of long hospital shifts, sleepless nights, I know I’m about as much use to anyone as a third-wheel on a date.

Modern day healthcare loves to put a number on things: we must exercise 150 minutes each week, our total cholesterol must be less then 5 mmol, and we should drink 2 litres of water a day - I mean, the list is endless. What about sleep, though? This is a very interesting question, since the answer is that scientists are not really sure. The National Sleep Foundation recommends you get between 7 to 9 hours of sleep per night. Now I don’t know about you but I can’t remember the last time I had 9 hours of sleep (even at only 31 years of age, my bladder refuses to let me, sadly). And of course, the frontiers of science continue to march forward; scientists in the US are working towards what they suspect is a more precise (and possibly lower) answer to the question, reflecting our evolving 24 hour habitual patterns of activity.

So as you read this, perhaps through weary eyes and sluggish brain, you may find yourself wondering how you can achieve a better night’s sleep. Sadly, there is no miracle cure but rather a very common sense set of principles, called Sleep Hygiene, that you can follow. These principles may help you to control the behavioural and environmental factors that precede your sleep. If you were to manage to implement these, ok, you might not create an Indonesian yoga retreat with whale music, but you may just make your bedroom and mind a cleaner, more uncomplicated, sleep-inducing environment to promote more restful, effective sleep. This can, in turn, endorse better daytime alertness.


Now, “I can’t sleep, doctor” is a common presentation to general practice, and, is often punctuated with “can I have something to help me sleep?” Although over 10 million prescriptions are issued for sleeping tablets every year in England, sleeping tablets are not panaceas to poor sleep. They do, however, have their place in management for you if you are suffering true bout of insomnia resistant to non-pharmacological treatment. Even then, though, this is ideally given only for a short period of time owing to the risk of dependency, increased tolerance, and next day drowsiness.

Finally, I wanted to touch on something that many of us love – a nap. The nap has been shown to enhance your information processing and learning, and increase your alertness and motor skills. Importantly too, it helps avoid ‘burnout’, that irritating, frustrating, poorer performance you may experience with mental tasks.

It is thought that the networks of neurones within your brain, and in particular your visual cortex (the part associated with vision), become gradually saturated with information through repeated mental engagement during the day. This saturation reaches a threshold where it prevents further brain processing, and so, you then experience ‘burnout’. This can be seen as your brain’s safety mechanism - like a pressure-release value. For that state of ‘burnout’ then allows for the preservation of information that has been ‘processed’ but has not yet been ‘consolidated’ into memory during sleep – the final stage of your learning.

So, if you just want a rest, opt for a 20 minute ‘power-nap’. If you want to lay down some memories and consolidate your learning, then you need a 60 minute ‘consolidation’ nap, for this takes you into your REM sleep where memories are deposited. Oh yes, and if you are wondering why you can sometimes wake up more tired than before the nap, it is because you have broken a sleep cycle too soon. This post-nap lag, known as ‘sleep inertia’, will pass with time.

Right, before my article becomes too long and sleep-inducing, let us summarise. Sleep is a fundamental, functional, and fascinating part of your 24 hour lifecycle. Poorly understood, it functions to help you refresh, recharge, and cement learning and memories. Disruption to it can be potentially devastating and leave you drowsy with poorer physical and cognitive functions. The good news is that you can take charge of it, perhaps by implementing some sleep hygiene principles – the most important of which nowadays, is probably to switch off your phone. As always, if you have any concerns please see your GP. Right, time for a nap…

Dr Nick Knight is a junior doctor based in London with a PhD background in human performance. His blog on life as a doctor can be read at: https://drnickknight.wordpress.com/

Or follow him via Twitter: @Dr_NickKnight