Fun sleep facts

This will be a place for, you guessed it… fun sleep facts! Interesting little tidbits about sleep that maybe you didn’t know.

I’ve already found one: the Sleep Paralysis Demon. Ever be dreaming and have the feeling that you’re under some kind of horrible threat, but you’re unable to move? Well, it’s got a name!
As an aside, this used to happen to me fairly often, and I finally learned how to just force myself to move. Just by straining really hard until I finally broke free to fight back. Sometimes this worked a little too well, however. Once I punched the wall. It hurt. :/