"But Mr. Blog," you might say, "surely sleep is just a mechanism that can help us preserve energy or get us to hide at night from predators or something." Yeah, maybe, but you're probably wrong. In fact, sleep only slows down metabolism by about 5-10% on average, and you could probably swing that just by watching infomercials all night. In fact, you can often preserve metabolic energy more efficiently by just sitting still than by sleeping, with the added benefit (in case of predators) that you wouldn't be unconscious and possibly snoring loudly.
But then there's the part where we would die without sleep. Don't be too afraid of that, though. You're body literally will not allow you to stay awake long enough to kill yourself. It forces itself to shut down momentarily in a process called microsleep, which occurs completely without warning when you suffer from extreme sleep deprivation. Your body takes over and forces you to sleep for about 1-30 seconds out of the blue. You'll still be miserable (and probably hallucinating), but you'll be alive. I'll let you work out the major disadvantages of the process for yourself.
|Here's a hint, though.|
|It's that protein, if you're interested.|
So to sum up: sleep is an almost completely unexplained phenomenon, and we don't know why the hell we do it, but without it, we die a prolonged, horrible death.