What is sleep?

Sleep is a temporary state of altered consciousness and significantly reduced susceptibility to signals from the outside world. The brain turns inward and engages in reconstruction processes. Sleep differs from unconsciousness in the way that a sleeping person is able to wake up, albeit with greater means than what's necessary for an awake person to react. Phenomena such as closed eyes, a lying position and immobility is part of the image of sleeping, but none of them is unique for sleeping – you can actually sleep with open eyes or walk in your sleep, although it's rare.

Why do we sleep?

It's not by chance we sleep 1/3 of the day. Nature is rational and makes every effort to maximize the survival of the species. Sleep function is actually quite simple. What we've exhausted and worn out during the day must be restored, and although much of the body can be restored during the day the brain is restored by sleep. The brain turns off all normal thought processes and ensures that the majority of brain cells are engaged in recovery.

How does the brain know when to sleep?

The fact is that the more we use the brain, the more fuel is used and more by-products to the release of energy will circulate. So, sleep depends on how much you use your brain. It's roughly the same thing as eating after you've been physically active. Sleepiness is really just an expression meaning that the brain is trying to switch to sleep because we used it too much. The repeated attempts to shutdown is perceived partly as heavy eyelids – the brain is trying to pull down the curtain. This often feels uneasy and a little embarrassing – and of course lowers the functional capacity significantly. The attention ability decreases dramatically and the sleepy becomes fatal if he or she is doing a safety-sensitive task, such as driving. A large proportion of road accidents is due to sleepiness.