Let me tell you about something that used to happen to me–not a common occurrence, something I’d experience maybe three, four times a year. I’d awaken suddenly from sleep, lying on my back, staring upward–and unable to move. I could breathe, and I’m pretty sure I could look around and blink, but otherwise I’d be completely paralyzed: unable to move my arms, legs, or head; unable to sit upright. My mind would struggle against the paralysis, usually by forcing my head to turn to the left (always the left). Eventually, I’d be able to will my body to move.

It wasn’t until about eight years after my first episode that I learned that I wasn’t the only one who’d experienced such a thing. My then-girlfriend, who’d heard of the phenomenon, called it sleep paralysis.

Director Rodney Ascher and the subjects of his new documentary The Nightmare also experience sleep paralysis. But for them, it doesn’t stop there. The phenomenon is also known as “hag dreams” and folklore (both antique and modern) associates it with various sensations: hearing voices, seeing humanoid figures, the pressure of a hand pressed against the chest, the unshakable feeling of sharing the room with an evil presence just behind–and to the left–of the “sleeper.” Several of Ascher’s subjects report seeing “shadow men,” and one interviewee delineates an entire hierarchy of such beings. Another tells of seeing slender, lanky humanoids, with skin like television static and faces like the “gray” aliens popularized by science fiction and UFO lore. Each of these men and women is a vivid dreamer, suffering nightmares that leave them doubting their own sanity.

What is sleep paralysis? Is it a biological condition, or is it metaphysical in nature? Are these figures imagined, or are they real? If the latter, are they from other worlds? Other dimensions? Angels and demons? Medical science doesn’t seem to have any answers. Each of Ascher’s subjects has a different theory. One perceives them expressly as demons in the Christian sense; she drove them away by invoking Jesus’s name. Another indicates that no amount of prayer would save him from his tormentors, and sees them as an unknowable force pulling him, inexorably, to his own death. They struggle to uncover the meaning of what they experienced. Like the subjects of Ascher’s previous effort, Room 237, each looks for a pattern to explain that which seems to have no explanation.

Ascher touches upon nightmares and the influences they’ve had on our culture, by viewing old woodcuttings and bookplates and splicing in clips from A Nightmare on Elm Street, Insidious, and Communion. But he puts more focus on presenting the nightmares in visual terms, presenting them as if they were literal horror movies instead of ones of the mind. Many of the tactics he uses are cheap shocks and jump-scares, but he deploys them so effectively he could probably teach a class about it. (The “giant insect of the month club” scene still freaks me out, after having watched it three or four times!) It’s the rare horror film that can work on several levels: the emotional, the visual, the existential. To call it one of the scariest movies of recent years is probably hyperbole…but I can say that it’s the first film I’ve seen in three or four years that’s genuinely given me sleeping problems, and I watch horror films like some people drink coffee.

If there’s one disappointment I have in The Nightmare, it’s that it possesses relatively little insight. No surprise there: its topic is a mystery that has no solution. As for myself, I haven’t had an episode of sleep paralysis in several years. Watching this film has made me grateful for that.

The Nightmare will be released in theatres and on VOD on Friday, June 5th.