Did you know you go on a journey every night after you close your eyes? Sleep scientist Matt Walker breaks down the difference between REM (RapidEye Movement) and nonREM sleep, what occurs during each stage of sleep and why it's important to get enough of both.

Sleeping with Science, a TED series, uncovers the facts and secrets behind our nightly slumber. Check out more episodes on TED.com: https://go.ted.com/sleepingwithscience