Train to Busan, The Wailing, A Tale of Two Sisters, I Saw the Devil — the Korean horror movies that have crossed over and popped in the States have been intense, often sprawling films that teeter on the edge of thriller. Their nightmares linger.

So Sleep, now in U.S. theaters, was an immediate surprise, simply by being a Korean horror movie with a playful rhythm. Think the heightened naturalism of Bong Joon-ho’s Parasite or The Host… but weirder. The feature debut of Jason Yu (whose previous credits include working as Bong’s assistant director on Okja) chronicles what happens to a newlywed couple when one partner’s sleep disorder takes the shape of a violent ghostly possession — and it may actually be one. As Yu explores the fallout of the situation, Sleep careens from domestic drama into the bizarre, in often funny ways.

Soo-jin (Jung Yu-mi of Train to Busan) is a business executive and the breadwinner for her growing family. Her husband Hyun-su (Lee Sun-kyun of Parasite) is a struggling actor, nervous about the shaky ground under his professional feet as he prepares to become a father. But Soo-jin believes in him, and wants to support him, even amid the physical challenge of pregnancy. She always goes back to the mantra that hangs on a wooden sign in their apartment: “Together we can overcome anything.”

With warm yellows and tender staging, Yu’s style amplifies the loving safeguard around the couple, which is then immediately shattered by the worst case of sleepwalking you could possibly imagine. Soo-jin wakes one morning to find Hyun-su with a nasty scratch across his face. The next night, she catches him wandering the house, devouring raw meat and eggs. Doctors diagnose him with a severe parasomnia, but one that can be cured through safety measures and drugs.

But like a horror version of Mike Birbiglia’s Sleepwalk with Me, Hyun-su can’t be contained and inches closer to deadly self-harm with each passing night. Soo-jin loses sleep agonizing over her husband, and then the baby is born, adding to sleepless nights and the potential targets for the “monster” living in their home. Sleep imagines what it would be like if you went to bed knowing every night Michael Myers could wake up next to you.

Yu finds the room to plunge into Soo-jin’s psychological situation, that of a supportive wife during the day and a protector at night, never sleeping, slowly unraveling. Jung Yu-mi masters the red-stained eye flicker that made Essie Davis’ performance in The Babadook so primal, and the friction sparking between the couple — even while one half is asleep — becomes utterly tragic. Then Yu swerves.

[Ed. note: some minor spoilers for Sleep follow, but if you want to just go watch this movie right now, we won’t blame you.]

The suffocating tension of the moment leads Soo-jin and her mother to wonder if there’s more going on with Hyun-su meets the eye. So they consult an exorcist, Madame Haegoong, whose energy is pure Tangina Barrons from Poltergeist. She claims there’s a spirit terrorizing their home through Hyun-su’s body. And he won’t stop. Whether there’s a ghost or not, as long as her husband’s sleepwalking persists, Soo-jin knows one thing is true: everyone in the apartment is in danger.

There’s more under the surface of Sleep, with Yu drawing from every genre element he can in order to unnerve and tickle. There are laughs to be had as Soo-jin descends deeper into supernatural theory and Hyun-su wakes up bright-eyed. (I screamed as one of the all-time greatest PowerPoint presentations was delivered late in this film.) But Yu never lets up on the peril either; the night shade of Hyun-su needs to be stopped.
Sleep feels like a major debut by a filmmaker who is ready to defy conventions and entertain audiences. It belongs alongside those great Korean horror films, even while standing apart.

Sleep is now in theaters and rentable on digital platforms like Amazon and Apple.