For seven or eight hours per day, we go into a profoundly different state – a system – shutdown, if you will. But how much do you really know about sleep, about why we need it and what happens while we have our nightly shuteye?

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See how many of the following facts you knew:

• During a normal night's sleep, there are five different stages of sleep – and each of them is quite different from the other four.
• When we are sleeping deeply, our breathing, our heart rate and blood pressure reach their lowest levels of the day.
• While we are dreaming, we experience REM – rapid eye movement. This is a very active time for both the body and the brain.
• While we are dreaming, our brain patterns are similar to those we experience while being awake.
• Most adults need about eight hours of sleep to function at their best, but studies have shown that most adults don't get much more than seven.
• We sleep more lightly during the second half of the night than during the first.
• Cats sleep up to 18 hours a day, giraffes usually not more than 20 minutes.
• Your body is on a 24-hour body clock, which makes you wind down between 1 a.m. and 6 a.m. and again in the three hours directly after lunch. We are really made to have siestas.
• It is more difficult to wake a child than an adult from deep sleep – often children will be disorientated and have no recollection of this later.
• Many people who suffer from insomnia suffer from anxiety and depression.
• Our large body muscles are paralysed while we sleep – most probably to stop us from doing what we are dreaming about.
• We go through four to six sleep cycles during a good night's sleep, moving through the different stages and back again.
• The average person wakes up about six times per night.
• Your body temperature falls in the early morning hours, reaches a low at about 4 a.m. and then rises again just before sunrise.
• Researchers have never been able to agree exactly why the body needs sleep, except that it is restoring to our bodies and our brains.
• Even when we are sleeping very deeply, there is still a part of us that picks up sounds and signals from the world around us. That's why parents wake up when the baby cries, but they don't hear the howling southeaster.
• Women and older people most often suffer from insomnia.

(Health24)

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