Lack of sleep will drive you crazy quicker than most anything, doctors tell us. And what your sleep partner is doing to interrupt that sleep just speeds up the process.

That’s the premise of the Korean thriller “Sleep,” about a couple waiting for a baby, struggling to get enough sleep to keep them sane and what happens when they don’t get it.

In writer-director Jason Yu’s slow slow SLOW burn debut feature, supportive, practical partnering and medicine run up against superstition in a tale that begins mildly and finishes in a fury.

Soo-jin (Jung Yu-mi) is a pregnant cubicle worker. Hyun-su (Lee Sun-kyun) is an actor, a bit player, living from small role to small role.

Late one night, he sits up, announces “Someone’s inside“(in Korean with English subtitles), and promptly flops back to sleep. After she’s the one left to frantically search their flat in the dark, rattled by the odd loud noise, they try to figure this out in the AM.

Is it from a script he’s memorizing? Probably.

But as nights go on, Hyun-su sleep-walks up to a window he tries to jump through, wakes-up bloodied by scratches and loses work because of his issues.

Is this safe for the baby to to be born into? Is it safe for their Pomeranian?

When they finally get to a doctor, “REM sleep disorder” is the diagnosis. Her mom (Lee Kyung-jin), seeing this growing distress as “grounds for divorce,” has another idea.

“He needs divine intervention.”

Yu’s script lurches from the comic — an over-the-top shaman (Kim Keum-Soon) bowls in and bowls them over with her diagnosis — “ghost” — and prognosis, to the grimly tragic.

Dreams turn dark and menacing and spill over into reality, especially after the baby is born, as Hyun-su’s”medical” treatment seems to work and she starts imagining their infant in every trash bin, every boiling pot of soup.

There’s little that one could call “psychological” in their analysis of the problem, but a little more in the way of questioning the nature of their relationship.

And once the supernatural is suggested, with all the Korean “rules” about ghostly possession and what-not, who is sane and who isn’t is kind of up in the air.

I found the early acts boring with moments of shock. But the finale to “Sleep” is a corker and well worth Yu’s perhaps unintentional efforts to encourage the viewer to doze-off. That climax is a waking nightmare of the worst-fears-confirmed variety. Whose worst fears? Watch and see.

Rating: unrated, violence, profanity, innuendo

Cast:Jung Yu-mi and Lee Sun-kyun

Credits: Scripted and directed by Jason Yu. A Magnolia/Magnet release.

Running time: 1:34