Many people don’t get enough shut-eye each night – there’s just not enough hours in the day to get everything done sometimes, and sleep ends up suffering.

But when it comes to sleep deprivation – we’re talking several days without a wink of sleep – what happens to the body when denied a basic biological need that no amount of coffee can solve?The longest amount of time a human has gone without sleep is believed to be about 11 days, or 264 hours – this world record was set by a 17-year-old high school student called Randy Gardner in 1965, when he forced himself to stay awake for a science fair project.

While no human is known to have died through lack of sleep (although a Chinese man was found dead earlier this year after reportedly staying up for 11 days to watch Euro 2012 football matches), the same cannot be said for rats. An experiment appeared to show that 32 days of total sleep deprivation killed all the rat subjects, although researchers did not agree that lack of sleep was certainly the cause of death. One idea was that sleep deprivation lowered the rats’ body temperature to the point where they succumbed to hypothermia, while another theory suggested that weakened immune systems left the rats vulnerable to the bacteria normally kept in check in their intestines. Another explanation was that the sleep-deprived rats suffered brain damage, or that high levels of stress led to their death.

So what happens when human beings are deprived of sleep? Pulling an all-nighter can actually leave the person feeling fairly awake, with research showing that the sleep-deprived brain becomes more active for a certain period of time. But beyond the first 24 hours or so, other factors come into play. Prolonged bouts of total sleeplessness lead to the person’s body temperature dropping, the immune system becoming depressed, and less able to fend off infection, impaired judgement and, in extreme cases, paranoia and hallucinations. I heard of a case where, during training, a soldier deprived of sleep started barking orders at a tree, becoming increasingly irate at what he took to be a lower-ranking officer stubbornly refusing to carry out his commands.

Sleep will out, no matter how much coffee you drink

Sleep deprivation is often part and parcel of a soldier’s life in war zones. Heavy fighting may mean that sleep is sporadic or non-existent. The effects of lack of sleep is a serious issue for the armed forces, where exhaustion can lead to poor decisions in life-or-death situations. This has prompted the military to commission research into ways of keeping sleepiness at bay, looking at drugs to keep soldiers alert and active.

The origins of why we sleep are still mysterious, and we still can’t be sure why we need to ‘push up zzs’ at all. The most commonly-cited reasons for needing sleep include memory consolidation, involving transferring memories to different parts of the brain in order to reorganise and restructure them, something creatures can’t do during waking hours when they’re meant to be on the watch for predators or finding food.

Genetics has shown that some people cope better with lack of sleep than others – finally a good excuse for people made to feel lazy by their more sprightly counterparts.

Thomas Edison, developer of the light bulb, claimed that sleep was a waste of time, “a heritage from our cave days”. Regardless of what the lighting pioneer felt about it, there’s no getting around sleep – biology demands it. And when it comes to hitting the pillow, I’m with the poet Samuel Taylor Coleridge: “Oh sleep! It is a gentle thing, beloved from pole to pole.”