This disturbing documentary about sleep paralysis comes from Rodney Ascher, the director who made Room 237 (2012), an anthology of heretical interpretations of Stanley Kubrick’s The Shining. In a comparable spirit he interviews people who suffer from sleep paralysis – a condition that flies under the clinical radar. People can have it all their lives without getting treatment or sympathy or understanding of any kind. The sufferer experiences an inability to move, often with vivid dreams, night terrors and hallucinatory visions: there are shadowy intruders, often with red eyes, sometimes squatting stiflingly on your chest. Ascher makes a persuasive case that it is the physiological phenomenon of sleep paralysis that has created the nightmare tropes now commonplace in art and literature: they are recognisable, diagnosable symptoms. This condition, he says, both pre-exists and is the inspiration for scary movies such as Nightmare on Elm Street – and not the other way round. It also accounts for alien-abduction delusions. However, his film also listens sympathetically to sufferers who interpret their condition in spiritual terms. He films his interviews and reconstructions in a self-consciously creepy way; it’s possibly a bit overdone, but often disturbing, especially the dream where the man gets a call on his mobile phone from a polite voice saying: “I wonder if you can do me a favour?” I jumped.