You curl up in bed and dream a little or not, snore a bit or a lot, and eventually wake up well-rested, but most often not.

As another hectic semester begins and your alarm clock chides you awake once again, it’s likely you’ll find yourself complaining in a half-conscious drunken slumber. Whether that’s because you’ve pulled an all-nighter or gone on a four-night bender, most of us (or perhaps just the less organised of us) spend at least part of our semester somewhat sleep deprived.  

Sleep is the first thing to go in the 21st Century, where incadescent light bulbs, smartphones and laptops are on far past our biological bed time. Thomas Edison, a man who believed his light bulbs should never go out – and a self-loathing power napper, wrote that “sleep is a criminal waste of time” and “there is really no reason why men should go to bed at all”, a notion that rings right along the lines of ‘sleep is for the weak’.

You’ll probably spend more than a third of your life asleep, assuming that you’re not a chronic insomniac. But the fact that we spend so much of our lives in this semi-comatose state, we hardly give it a second thought. If the average person spends 32 years of their life in repose, it’s obviously kind of important.

Whether you see it as a necessary evil or dream of living the burrito life, the question remains: why is it necessary? When we’re sleep deprived, we go a bit crazy, get a bit cranky and struggle with the most menial of tasks.

What exactly is going on when you’re sprawled across your mattress, one foot out from under the cover, socks displaced and mouth agape?

Not much, it would seem to the casual onlooker.  

There are a whole host of theories floating about as to why we sleep but scientists have yet to reach a consensus (as with most things).

One fairly convincing theory is that we sleep to conserve energy. Whilst that sounds logical it’s not at all the case. By getting a good night’s sleep, it’s estimated that you save yourself a whopping 110 calories. That’s the equivalent of a slice of bread.

A more convincing theory is that we sleep to restore what was lost during waking hours. Neuroscientists have recently discovered that there are genes that only switch on during sleep, these are associated with restorative pathways such as muscle growth, tissue repair and protein synthesis. Scientists from Surrey University conducted a study in which volunteers were separated into two groups – one which slept for less than six hours a night for a week and another which slept for ten hours a night. By studying blood samples from both groups, they found that sleep deprivation altered the function of 711 genes – whose functions ranged from regulating metabolism to immunity and stress. But rest assured, a week’s worth of normal sleep was enough to reverse this genetic short-circuiting.

The theory that memory consolidation is a function of sleep is gaining traction within the scientific community. Results of several studies suggest that sleep allows us time to reconstruct our waking experiences. When mice were trained to work their way around a maze, their brains showed the same pattern of activity during sleep as when they carried out the task. You may have experienced this yourself – have you ever played so much Tetris that you continued to play it in your dreams? I (shamefully) can say that I have.  

Jan Born and Ulrich Wagner, a neurobiologist and neuroscientist respectively, posed a relatively complex math problem to a group of people. It seemed an arduous task, but by the use of an abstract rule, there was a very simple solution. A few of the participants were able to spontaneously solve the problem on the first attempt. The rest were re-tested eight hours later – some of the group had to remain awake, whilst others were allowed to sleep. Less than a quarter of the sleepless group figured out the quick solution but sixty per cent of the participants who had slept gained the insight into the shortcut. The insight rate had more than doubled amongst those who had spent the eight hours sleeping. This is just part of the surmounting evidence showing that sleep plays a vital role in replaying, processing and learning.  

Sleep also plays a more vital housekeeping role in our bodies. Recently, a group of scientists led by Professor Maiken Nedergard at the University of Rochester found that when we sleep, the brain gunk – like toxins and unused proteins – that accumulates throughout the day is cleared out.

As Professor Nedergard says, “You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”

So why do we sleep? When I asked my mum the same question, she responded indisputably: “We sleep because we get sleepy”.

As of now, that’s probably the most conclusive theory we have.