In The Nightmare, director Rodney Ascher (Room 237) has done just that. The film explores the condition commonly referred to as “sleep paralysis.” That’s a condition where someone is in bed, but totally physically immobilized. Some who suffer from the condition – including the eight subjects in this documentary – feel they are visited by something evil during these periods. Ascher lets these subjects tell their stories, then we watch them play out on screen. It’s absolutely horrifying, if not wholly rewarding.…