Why sleep?

While we are awake, the higher centres of the brain are working flat out. Even lying down, the brain is in a state of quiet readiness, ready to respond. The only time it can rest is during sleep. Sleep is important because we know that, even when people know they will die if they go to sleep. Like shipwrecked sailors or overtired pilots, they still do so. Nature has provided nothing that overrides this

Professor Jim Horne [15]