One-third of our lives we spend asleep. An alternate dimension, sleep is the land where dreams occur, sweeping us into a surreal logic unknown to our waking selves. Like all animals, humans need sleep, along with food, water, and oxygen, to survive. Apparently, our minds need to travel to the unfamiliar spaces beyond consciousness in order to stretch their legs a bit.

Chinese artist Zhou Jie
(Chinese artist Zhou Jie) Here, artists render a variety of sleep disorders, including night terrors, paralysis, sleepwalking, and narcolepsy. Jason Lee for Reuters