The random film of the day took us back to 1987, to the third installment of A Nightmare on Elm Street: a psychiatric hospital, teenagers with diagnoses, and a killer with a burned face who comes for them in their sleep. Freddy Krueger is the perfect monster of his era—he has no weak spot: you can’t kill him in your dreams, and you can’t not sleep, physiologically speaking.
What’s more interesting is where Wes Craven got the idea. Fifteen years earlier, in 1981, Craven needed a hit—his previous work hadn’t broken even, and he went off to shoot Fatal Blessing and Swamp Thing back-to-back, while already carrying in his head the idea of someone like Freddy. The detail that brought the idea to its final form came from the newspapers: all year long, the Los Angeles Times had been reporting on Laotian refugees dying in their own beds in their sleep. The headlines followed one after another: “Mysterious Fatal Malady Striking Hmong Men,” “Nocturnal Deaths of Asian Men Remain Unexplained.” One article contained a scene worthy of jagged horror: 47-year-old Yeung Leng Tao had moved to America with his family from a refugee camp in Thailand and died in his sleep within the first months of life in his new country; his wife found him beside her. The fourth Hmong man to die in nine months; the thirteenth nighttime death recorded since 1978.
Craven recalled (he retold this version in Vulture’s oral history) the story of a Khmer child who was afraid to fall asleep: he saw visions of a man who came in dreams and would not let him wake up. “The mother and father heard screaming in the middle of the night,” he said. “By the time they got to him, he was dead.” The versions differ—in some retellings the child is Khmer, in others the trigger was the articles about the Hmong—but the essence is the same: Craven himself later put it this way in a 1988 interview with Rolling Stone: “I just turned it around and said, what if the nightmare was real?”
The question was not a horror-movie invention. That same year, 1981—alongside the newspaper headlines Craven was reading—the U.S. Centers for Disease Control and Prevention introduced a name for the syndrome: SUNDS, Sudden Unexpected Nocturnal Death Syndrome. CDC physician Roy Baron described it with cool academic precision: “This is a totally new syndrome. Death of young, healthy people that occurs at night, occurs within minutes, and cannot be explained by autopsy.”
This is a story of how two explanations for the same phenomenon—one electrical, one ethnographic—moved toward each other for twenty years, until they converged at the point where they could finally be tested.
To understand why nighttime deaths were frightening specifically as deaths in sleep, we need to remember what REM does to the body.
REM sleep is not “deep” sleep but, paradoxically, the most aroused kind: in terms of activity, the brain resembles a waking one. But at that moment the body is switched off: brainstem structures inhibit motor neurons, and skeletal muscles are rendered atonic—a protective paralysis without which we would physically act out the plots of our dreams. If the boundary between REM and waking is disrupted, a paradox occurs: consciousness has already awakened, but the body has not. The person waking up cannot move, cannot cry out, breathing is restricted—and, more importantly, the dream’s narrative “frame” has not yet been dismantled: the scene keeps playing against the backdrop of paralysis.
This condition is called sleep paralysis, and it produces a clinically recognizable picture. According to a 2024 review published in Cureus, more than 75% of sleep-paralysis episodes involve not merely terror but structured hallucinations: the sense of an alien presence in the room (intruder), pressure on the chest and suffocation (incubus), and vestibular-motor phenomena—the sensation that the body is moving, leaving itself, falling (vestibular-motor). The triad of “someone is in the room, pressing on me” is so reproducible that researchers are essentially describing the same scene humanity has been staging for centuries under different names. REM’s paralyzing muscle atonia, “leaking” into wakefulness, is considered the main mechanism.
Its prevalence is hardly exotic: under 8% in the general population, but 28.3% among students and 31.9% among psychiatric patients, slightly more often in women. And as for the Hmong—and not only them—sleep paralysis has a cultural map, with its own nomenclature of ghosts: the European “old hag sitting on the chest,” the Filipino “bangungot,” the Thai “Lai Tai.” Deaths in sleep had names in every culture long before the CDC.
Hence an important clarification for what follows: “something is pressing on my chest” is a real, physiologically credible phenomenon, and almost always harmless. The question that interests us is how this phenomenon came to kill someone.
The chain of medical observations begins not with the CDC, but with Los Angeles. From the late 1970s onward, Los Angeles Times reporters went from house to house among Hmong families, documenting those who had died in their sleep. By December 1981, the Associated Press was already tallying 38 cases between July 1977 and October 1981. A May report in The New York Times named 18 Laotians who suspected nightmares were the cause. In December 1981, the MMWR—that same Morbidity and Mortality Weekly Report that nowadays people read like an omen—fixed the definition: “Sudden, unexpected, nocturnal deaths among Southeast Asian refugees.” The acronym SUNDS entered circulation.
The epidemiology was textbook in its pattern—which is to say, not random. By August 1988, the CDC had counted 117 cases under surveillance since 1981. A review of thirteen fresh cases yielded a portrait impossible to mistake for statistical noise: ages 19–57, median age 33; all the dead were men; nine of thirteen were Laotians, including five Hmong; twelve of thirteen deaths occurred at night or during sleep. Of all 117 whose migration history could be reconstructed, the median time spent in the United States was 17 months. The overwhelming majority died within their first two years after arrival.
The epidemiological outline came together too: around 850,000 refugees from Southeast Asia lived in the United States; arrivals peaked in 1980—151,000 people—and by 1987 had shrunk to 36,000. By 1987, the outbreak was nearly running out of breath: the CDC recorded 5 deaths, and in the first four months of 1988, 2; the crude mortality rate among Southeast Asian men—1.1 per 100,000—was the lowest since 1976. So at the time of the premiere of Dream Warriors, the very wave that had suggested Craven’s plot was already receding, and it would have receded even without any flaw in Freddy’s character. By 1988, death of “young, healthy people at night, within minutes, with no explanation after autopsy” was no longer an epidemic—but it had not ceased to be a mystery.
The first explanations, meanwhile, were not metaphysical at all. In 1984, Otto and colleagues published a paper in Annals of Internal Medicine arguing that sudden deaths in Southeast Asia were ventricular fibrillation. In 1986, a study by Kirschner, Eckner, and Baron in JAMA uncovered cardiac pathology in the dead. In its 1988 update, the CDC stated plainly: structural abnormalities of the heart’s conduction system and stress had been studied as risk factors, but the cause of the deaths remained unknown. Formally, the CDC was looking for a body among refugees that could kill from within.
The next turn came neither in America nor in a director’s office.
Deaths in sleep turned out to have a remarkably broad geographical presence, and each place called them something different. In northeastern Thailand—“Lai Tai,” literally “to dream or cry oneself to death in sleep”; in Japan—“pokkuri,” “death during sleep” (systematic pathological studies of the phenomenon date to the 1950s–1970s); in the Philippines—“bangungot,” where bangun means to rise: according to Filipino accounts, the victim wakes in the middle of the night after a heavy dinner, gets up and groans, and if he is not awakened—dies. Cases of Filipino bangungot were described as early as 1917 in a Spanish-language medical publication; 460 autopsies conducted in the Philippines between 1915 and 1938 provide a stable portrait: men aged 25–40, in perfect health the day before, with “a heavy meal or cheerful spirits” the previous evening. In 2018, the Journal of the American Heart Association would call it “a hundred years of mystery”—a century of observation without the case being closed.
The case was closed in 1992. Pedro and Josep Brugada described the syndrome that took their name: a triad of conduction abnormality, ST elevation in the right precordial leads, and fatal arrhythmias—essentially, an ion channel in the heart that under certain conditions can no longer hold the rhythm. Thai researchers who had been studying Lai Tai since the early 1990s matched the symptoms and reached the conclusion that tied the whole map together: SUNDS and Brugada syndrome were the same disorder. The SCN5A gene was found in three out of ten families; yet more than 90% of Thai patients had no mutation in this gene, and today the syndrome is considered polygenic, with a range of modifiers and, in the Thai population, a founder effect for the p.R965C variant.
Mechanically, the picture is this: sodium current in the heart is weakened, and a series of triggers can send the electrical system into fibrillation. The list of triggers, incidentally, almost word for word matches Filipino folklore: fever, alcohol, vagotonic states, sodium-channel blockers—and, of course, heavy food intake, that same “heavy meal” in descriptions of bangungot. Where folklore saw “cheerful spirits,” cardiology saw the vagus nerve. No mysticism—just a coincidence of lists that reads like mysticism only because the lists were written in different centuries.
As for proof that this really is an electrical death: from 1996 to 2000, Thailand ran the randomized DEBUT trial—implantable defibrillator versus propranolol in 86 survivors and probable patients with SUDS/BrS. Over three years of follow-up, not a single death occurred in the defibrillator group (though the devices fired in 26% of patients there, knocking back episodes of fibrillation), versus seven deaths (18%) in the beta-blocker group; p = 0.02. The study was stopped early in December 2000, and five years later the Thai state began paying for these devices for SUDS/BrS patients. The monster that comes in sleep turned out to be a heart knocked out of rhythm by current.
The second explanation ran in parallel—and it cannot simply be dismissed as superstition, because it grew into a serious research program.
The Hmong themselves already had a name ready for nighttime death: dab tsog—an evil spirit that comes and strangles the sleeper. Similar “pressing ghosts” exist in European, Filipino, and Japanese traditions; researchers have long linked this body of folklore to sleep paralysis—the very picture of “someone in the room, on my chest, choking me.” The problem with the explanation that “the spirit killed him” was arithmetic from the start: in Laos, dab tsog attacks were regularly described, while deaths were extremely rare, almost unheard of. The spirit had to become a killer specifically in America.
Shelley Adler, a researcher at the University of California, San Francisco, spent fifteen years doing fieldwork on the problem, interviewed 118 Hmong people in Stockton, California, and ultimately formulated a thesis that sounds calm today but was provocative then: what killed was not belief in the spirit as such, but the way belief works as a nocebo. The dark side of placebo: an expectation of harm, accepted literally enough, can cause real physiological damage. Adler developed the argument into a book in 2011 (Sleep Paralysis: Night-mares, Nocebos, and the Mind-Body Connection). Adler is more careful than popular retellings, though: her point is not “spirits killed the refugees,” but that the stress of traumatic relocation, the lack of cultural infrastructure for processing fear, and a substrate that was likely cardiac came together in a single chain. The argument about culture is supported by comparison: in Laos, experiencing dab tsog attacks was ordinary and did not bring fatal consequences; in America, in a state of isolation and chronic stress—it did.
There are also direct data standing between folklore and cardiology. A case-control study in the Ban Vinai refugee camp in northeastern Thailand (Am J Public Health, 1987) found 16 sudden deaths in sleep resembling the American cases, and three associations: belonging to the “Green Hmong” subgroup, a family history of sudden death, and prior—nonfatal—sleep disorders. In other words, the picture of a sleep-deprived, tense person carrying a familial cardiac burden was reproduced independently of the American context. And the family history is precisely what you would expect in a case genetically converging on Brugada: from an ion channel that is inherited.
A historical note to the “belief kills” version: the idea itself is not new. In 1942, physiologist Walter Cannon described “voodoo death”—cases in which a curse, taken literally, killed a person—and defined it as “the fatal power of the imagination acting through unmitigated terror.” In Adler’s hands, SUNDS became a modern continuation of that line, only instead of a sorcerer in the forest, there was a spirit sitting on the chest, and instead of a tribe, a bedroom in Stockton where a family had arrived from a camp.
It is worth assembling the chronology to see the shape of the era. Between 1977 and 2005, medicine asked three times: can sleep itself kill a person?—and three times received different answers that did not exclude one another.
1977—the first death entered into the CDC archive among those that would be called SUNDS. 1981—the CDC introduces the definition; Craven reads the Los Angeles Times. 1984—Otto and colleagues document ventricular fibrillation. 1986—The New England Journal of Medicine describes fatal familial insomnia: a prion disease in which the thalamus degenerates to such an extent that a person physically ceases to sleep and dies months later. “Death from insomnia” is, for the first time, not a metaphor. That same year, 1986, JAMA publishes the cardiac pathology of SUNDS victims. 1987—the premiere of Dream Warriors and, paradoxically, the lowest SUNDS mortality in the United States; the Ban Vinai study. 1992—the Brugada brothers describe the syndrome. 1995—Adler’s article on nocebo. 1996–2000—DEBUT. 2005—the Thai state begins paying for defibrillators.
This line does not close because the explanations work on different levels. If a person with weakened sodium current dies in fibrillation during sleep—the cause is electrical. If that same person, in the first months after a refugee camp, in a society where nighttime death has a ready-made name and a ready-made mechanism of blame, sleeps in a state approaching chronic sleep paralysis and stress—stress can become the trigger that sends the channel into fibrillation. The versions do not argue: one supplies the other with the trigger. When the CDC said in 1988 that “the cause remains unknown,” it was technically right—the cause turned out to be combined.
And there is one more plot worth keeping beside it, because it belongs to the same logical sequence: Freddy Krueger’s death and the death of a person with SUNDS frighten us for the same reason—the vulnerability of a state from which you cannot defend yourself through conscious action. Against Freddy, in the film, the heroes are helped not by strength but by control over sleep (banal as it sounds, the third installment is about therapy and consciously entering one’s fears). Against Thai death in reality, the help turned out to be equally banal and engineered: a device that delivers an electric shock in fractions of a second and pulls the heart out of fibrillation. The monster became manageable where it could be measured.
Incidentally, one fair caveat about Craven. His retellings of the story of a single Khmer boy differ from the Hmong newspaper chronicle; film historians rightly note that the plot may have taken shape from a series of articles rather than one. But that does not diminish the fact: Craven was the first to translate an unresolved medical phenomenon into the category of monster, and medicine spent the next twenty years translating it back—into a diagnosis.
Today, SUNDS has almost vanished from headlines, while BrS remains one of the known causes of sudden death among young men in Asia. This entire story, stripped of its names, is about the difference between what we see when something happens at night and what turns out to lie beneath the skin. Sleep does not kill. Sleep simply turns out to be the most vulnerable place where a spark can flare—and in that sense Freddy, a monster invented from a newspaper, remains an exact metaphor, only without the knife glove.