Isn't sleep funny? Infants seem to need it. Dogs seem to use it as an altenrative state of consciousness (like some people I know in boring meetings, concerts, sermons, family visits. They do it with eyes wide open.)
Sleep can refresh, terrify, end too soon as in getting up to pee several times in the night. It can go on too long, as in: Holy sh!t. I slept in. I'm LATE!
Sleep is mysterious. We know almost nothing about it. Oh sure, we know REM sleep and a few other things. We know synapses do stuff. But we really don't know much.
As Shakespeare said, to sleep perchance to dream. Dreams are part of sleep. We fix things up, we sort things out. We have NIGHTMARES!
Death is the big sleep. (I'm not going to go there)
We know we can feel like death walking if we get sleep deprived.
And finally, "There's nothing like a good night's sleep!"