Dreams

Judging by the amount of mental and physical stress that you receive each day is the amount of sleep one should get in a night. When you sleep, you dream. Most the time you don't remember your dreams, but your subconcious does and that's all that really matters. When you dream your emotions are balanced out from what you have in waking. The astral planes (dream world) are there to give you emotions you don't have in waking, to balance you out and keep you going. Which is why dreaming either sucks or is awesome. But its a necessity and it helps calm the spirit during stressful days. Of course, that's not the only purpose of dreaming, it's just the main ones for those who aren't open minded enough to see what else the astral planes have for one.