Why do we sleep?

well i heard somewhere when you rest (sleep) your body repairs itself and the human body needs rest hence the signs we get when we are tired. Try going the whole day with NO rest then you'll get your answer.

we need to sleep because it is in sleeping when our cells get to regenerate. regeneration of cells will keep us healthier. lack of sleep will result to illness usually inclined to blood deficiencies.

We sleep because we need to recharge ourselves. We're like computers and gadgets that loses power and thus needed to be recharged. Our system will die slowly if we abuse it

During sleep our body does many things that it cannot do as effectively while we are awake. For a start tissues heal while we are asleep - sprains and strains and stuff. Our brains 'compute' all the info we've taken in during the day during our sleep - that's partly what dreams are for. In addition certain chemicals are released mostly during sleep, such as endorphins, which are natural painkillers and anti-depressants. I suffer from an illness called fibromyalgia, in which I cannot get into the deeper levels of sleep were these endorphins are released, so I have chronic pain and depression problems.