You’re lying safely under the covers when a shadowy figure comes walking through the door. Terrified, you watch it pass the foot of your bed on its way to you. You want to escape but you’re pinned to the mattress. You begin to sweat, realizing as the figure comes within inches of your face there is no escape. It feels like the end.

But suddenly you wake up. Your heart is racing, but you’re safe, with no shadowy figures to speak of. What you just experienced was an episode of sleep paralysis: a phenomenon of semi-wakefulness in which the body’s limbs are still immobile from REM sleep, yet the brain has already started waking up.

Some populations experience sleep paralysis more than others (28 percent of college students, by one study’s measure), although the bulk of sleep paralysis research shows roughly eight percent of the general population reports at least one episode. People commonly report frightening hallucinations, intense nightmares and feelings of realness, and recurring characters intruding into their bedroom.

Perhaps the most common cause of sleep paralysis is disrupted sleep — lending to college students experiencing it more often — though it’s also been linked to narcolepsy, migraines, anxiety disorders, and obstructive sleep apnea. When there’s no secondary disorder, the phenomenon can fall into two categories: isolated sleep paralysis (ISP) and recurrent isolated sleep paralysis (RISP). ISP is the more common of the two, seldom lasting more than a minute or two. RISP, however, can last up to an hour.

Filmmaker Carla MacKinnon was so distraught by her own battle with sleep paralysis that she decided to make an “experimental docu-horror” film about her experiences, which she calls “Devil In The Room.”

“Throughout summer 2012, two or three times a week, I would wake up unable to move, deeply afraid and convinced there was someone or something in the room with me,” Mackinnon explains. “This strange phenomenon is called sleep paralysis, and I decided to make a film about it.”

Devil In The Room from Mackinnonworks on Vimeo.