I loved Rodney Ascher's Room 237, a documentary about peoples' wacky interpretations of Stanley Kubrick's The Shining. Now Ascher is back with a new doc called The Nightmare, which takes a look at a condition suffered by millions of people called sleep paralysis. The trailer does such a good job of explaining what that condition is — and the utterly terrifying things that some people see while they're in that state — that I'll just recommend you watch it to understand the full weight of what these people experience. Check out the trailer, and make sure to read our review of the movie from this year's Sundance Film Festival.