Is it any wonder that sleep has long been a topic for horror? It’s our most exposed and disoriented state. Sleep has been scary on-screen since the 1920s, beginning with German expressionist horror. In The Cabinet of Dr. Caligari, which depicts a brainwashed sleepwalker, or Nosferatu (including Eggers’ 2024 take on it), in which a vampiric villain uses sleep to manipulate as well as attack. Since, sleep has found its way into nearly every subgenre. In supernatural-slasher A Nightmare on Elm Street, Freddy Krueger hunts teenagers down in their dreams, one final threat to the fragility of childhood. In the found footage classic Paranormal Activity, sleep has been difficult for Katie her entire life thanks to a demonic entity tied to her familial history. In films like The Amityville Horror, sleeping and waking states give way to fears about domestic violence. In the Insidious series, the nature of sleep itself is a doorway for any sadistic spirit, and its parallels with mental health struggles and domestic violence culminate in a family rift that explores familial trauma in its latest entry, Insidious: The Red Door.

In 2023’s Sleep, director Jason Yu pushes the boundaries of these themes and vulnerability itself. Where other films have marriages collapse off-screen or explore states of possession as a means of domestic violence, Sleep stacks sensitive and susceptible states on top of one another. Blending dark comedy with the more common traits of Korean horror – familial tragedy, a personal portrayal of psychological terror, and social struggle – Sleep depicts sleepwalking states and demonic presence with ambiguity, and wields it against a family unit so warm and loving that even the most die-hard horror fan will find themselves begging for it to stop.

Real Mental Health Challenges Amplify the Scares in ‘Sleep’

Hyeon-soo (Lee Sun-Kyun, Parasite) and Soo-jin (Jung Yu-mi, Train to Busan) are a married couple very much in love. So in love, in fact, that with less charismatic actors, it might be a little insufferable. A wooden sign hangs over their portrait wall — which includes a wedding portrait with their little pomeranian – says, “Together we can overcome.” Hyeon-soo, a booked but less than successful actor, is a heavy sleeper prone to snoring. Soon-jin is his number one supporter, working full-time while pregnant, encouraging him to continue his pursuit of acting even when he offers to go into real estate, and so in love she finds the snoring endearing.

But Hyeon-soo’s sleep episodes worsen, just as Soo-jin enters late-term pregnancy. His behavior escalates to things befitting of a horror film in due time, but right away it’s extreme and disturbing. Hyeon-soo doesn’t take on the movements typical of K-horror. Instead, he is deeply human in his drowsy fumbling as he eats raw eggs, including the shell, bites the heads off of fish, and drinks directly from the kitchen sink wide-eyed and unaware that Soo-jin is trying to stop him. Where the uncanny valley seeks to take a step outside of what we recognize as human, Lee’s performance is so human that it makes his character’s feral, even harmful behavior more jarring.

His night escapades are in direct contrast to his daily persona. He is doting, loving, and light-hearted with Soo-jin. When their daughter arrives, he’s a perfect and patient father, attentive to cooking and cleaning while baby-wearing so that Soo-jin can rest and recover. The juxtaposition makes the escalation of his sleep disorder to dangerous behaviors even scarier. Soo-jin wouldn’t be losing an insufferable grouch or a father already phoning it in. She’d be losing her best friend.

A visit from a psychic medium uncovers evidence of the supernatural, but that’s not the film’s main focus. Symptoms of spirits or possession mingle with the very real symptoms of sleep disorders, and for Soo-jin, postpartum depression has more than usual to cling to. Sleep gives screen time not just to the horror of the night, but to the mundane challenges of the day. And it does so without painting either character as hysterical. Between Yu’s vigilant screenwriting and the ways Western horror primes audiences to view a horror movie marriage, the film’s tension comes as much from waiting for the other shoe in their marriage to drop as it does from rituals, relics, and violence. With chemistry between leads rarely seen in horror and a strong connection that holds this couple a far cry from the supernatural bickering and breakdown of most on-screen horror marriages, Jung Yu-mi and Lee Sun-Kyun breathe new life into universal tropes.

Everything but Love Is Ambiguous

Sleep is a terrifying exploration of both severe sleep disorders and postpartum depression or psychosis, and that’s before the supernatural ever gets in. When Hyeon-soo’s sleepwalking becomes dangerous, Soo-jin helps him set up a doctor’s appointment. She’s with him every step of the way, even when her mother offers support. When Hyeon-soo wants to sleep in another apartment, Soo-jin invokes their family motto, “Together we can overcome.” When Soo-jin’s mental health is exasperated by the notion of spirits or possession, Hyeon-soo agrees to see the psychic medium. In the particularly high-stakes moment of the film’s climax, when it seems like death could be very near, both Hyeon-soo and Soo-jin invoke the family motto in turns. Every ominous detail of the narrative is anchored by love.

It’s arguable that Sleep offers no clear answers between the supernatural, the inherent challenges of a long-term partnership, and the surprises mental health struggles can throw anyone’s way at any time. What is clear is how meaningful the support of our loved ones becomes. As struggles beget struggles, Hyeon-soo and Soo-jin take turns succumbing to the mania of whatever it is that haunts them, and so take turns supporting each other. At no moment in the film’s runtime is the audience invited to doubt the love they have for one another. Its sincere portrayal of love and marriage makes for an exploration of fear and trauma that resonates with anyone who has ever needed or wanted to give extra support.