As you drift off into a peaceful sleep, it seems there's just a blank nothingness – for a good eight hours or so until you wake up the next morning.
In fact, all manner of things are going on in your sleeping body without your conscious knowledge.
Here are 10 of them…
1. Your brain works better
Colin Espie, professor of sleep medicine at Oxford University, explains that far from having a nice rest while the body's sleeping, the brain is functioning better than ever thanks to the distractions of daily life being removed.
“Our brain probably functions better when we're asleep than when we're awake,” he says. “During the day you're mostly expending brain power living your day-to-day life, so the brain's main job of intelligent functioning and creating memory and capacity for the future is mostly done when we're asleep.”
2. Your body temperature drops
Just before you go to sleep, your body temperature starts to decrease slightly, as your brain releases the hormone melatonin. Normally, melatonin levels begin to rise in the mid- to late evening, remain high for most of the night, and then drop in the early morning. This affects your circadian rhythm (sleep/wake cycle), so increased melatonin means you're more sleepy.
3. Your memory improves
Slow-wave, or deep sleep, is critical for memory consolidation. Such sleep, which is usually during the first half of the night, stabilises memory from short-term to long-term. People with insomnia, who experience less slow-wave sleep than normal sleepers, have impaired memory consolidation.
”During the night when we're asleep, the brain does work for itself, consolidating memory, for example,” says Professor Espie. “There's lots of evidence that shows people learn tasks much better during periods of sleep than they do during equivalent periods of wakefulness. This is one of the reasons sleep is so important for our wellbeing.”
4. You lose 'weight'
You lose water through perspiring and breathing during the night, and although this happens during the day too, eating and drinking cancels out any difference on the scales. So that's why the scales will give a lower reading if you weigh yourself first thing in the morning.
5. You can see
“Sleepwalkers aren't blind,” Professor Espie points out. “You don't deliberately see. A great deal of what we do, we do automatically, and sleep is just one of those things.”
6. Your limbs jerk
Muscles can suddenly contract and the whole sleeping body may jerk. It's not clear why, although some experts think such spasms are connected to anxiety or irregular sleep patterns.
7. Your eyes move from side to side
During REM (rapid eye movement) sleep, your eyes dart from side to side. Professor Espie says that although it's not really known why this happens, it's thought to somehow facilitate information processing. “Even when people are awake, if they're thinking intensely their eyes scan, although it's not really known why that happens or why it happens during sleep,” he says.
8. You get taller
You gain height while you're asleep, as your spinal discs rehydrate and get bigger because the weight of your body isn't pressing down on them, You're not, however, likely to see the difference when you wake up!
9. Your limbs are paralysed
Professor Espie says dreaming sleep, or REM sleep, is characterised by an awake brain in a paralysed body. “It's your musculature that's paralysed,” he says.
“This is nature's way of preventing you acting out your dreams. It happens to animals too – you see the occasional eye movement and twitch in a sleeping dog, but they don't get up and chase rabbits in their sleep because they're paralysed.”
So sleepwalking, for example, occurs in deep sleep and not during the paralysis of REM sleep.
10. You can be awake and asleep simultaneously
“It's a bizarre truth about sleep that you can be awake and asleep at the same time,” says Professor Espie. “Part of your brain is clearly awake when you're sleepwalking because you're able to navigate your way around the room and you can see, but you don't know what you're doing, you have no memory of it, and you're hard to awaken from it.”
The University of Oxford is conducting an online study on insomnia. If you'd like to participate, visit www.sleepio.com/research/dials
What weird things have you done while asleep?