How is it that this state of inactivity or sloth pervades the animal kingdom? Wouldn't it be more evolutionarily advantageous to be active all the time? Couldn't an organism find a better meal, mate more often, and avoid predation more effectively if its waking hours were increased by a third or more? In retrospect, this primal need has affected my week in a most unpleasant way, causing me to go comatose while in the middle of doing things that require absolute focus. So, because of this, I have dredged up a number of articles in relation to the mystery of sleep, its purpose, and how to deal with its effects.
One article from the New Scientist summarises scientific hypotheses on why sleep is necessary, and why it can even result in death if some are forced to go without it. One commonly accepted hypothesis is that sleep is a way of "conserving energy" while darkness predominates and there is nothing useful to be done. Still, the energy savings of this sluggish period are relatively minimal, for a human it is something on the order of 200 calories saved.
Still, another examined hypothesis is that sleep is a mechanism for recycling chemicals in the architecture of the brain. It is suggested that this down-time allows for neurons to reset their chemical balances for another round of a day's work.
Last, there is something to be said for sleep's potential as a survival strategy. Some zoologists and naturalists believe that sleep is very effective at keeping an organism out of trouble. Still, in our modern lives it may lead to the exact opposite!
There is much more, but that's all I have time for