Director Rodney Ascher follows up his 2012 feature debut "Room 237," a documentary deconstruction of all the hair-brained close readings of Stanley Kubrick's "The Shining," with Sundance premiere "The Nightmare" about the terrified victims of sleep paralysis. Ascher, who has suffered the condition himself, lays out and interprets the nocturnal experiences of eight individuals plagued by malevolent, dream-state visions—and many are alarmingly similar.