"A Dead Body Climbed on Top of Me"— A Sign of Sleep Paralysis?

MINNEAPOLIS—“A dead body climbed on top of me” is an expression familiar to most Mexican adolescents, and the characteristics of such an experience suggest that it is nearly identical to those of sleep paralysis, according to Alejandro Jiménez-Genchi, MD, and colleagues. More than a quarter of all Mexican youth have reportedly experienced the phenomenon, suggesting that sleep paralysis occurs highly frequently in this group, the researchers reported at the 21st Annual Meeting of the Associated Professional Sleep Societies.

Sleep paralysis consists of a transient period of an inability to perform voluntary movements at sleep onset or during awakening at night or in the morning. Although epidemiologic studies in the general population have yielded sleep paralysis rates of 6% to 11%, previous studies of specific population groups have found lifetime prevalence rates that range from 4% to 62%. One such study found a prevalence of 11% in a Mexican population. “However, those authors used a clinical description to investigate sleep paralysis, while Mexicans use the expression ‘A dead body climbed on top of me’ to describe an experience that seems to be equivalent to sleep paralysis,” stated Dr. Jiménez-Genchi. He is Chair of the Sleep Unit at the National Psychiatric Institute and Professor of the Sleep Disorders Fellowship Training Program at the Autonomous National University of Mexico, both in Mexico City.

SLEEP PARALYSIS IN ADOLESCENTS

Dr. Jiménez-Genchi and colleagues evaluated 230 participants (71% females), all younger than 18, from three high schools in Mexico City. The mean age of subjects was 16, and the mean age at sleep paralysis onset was 13. “Considering that the onset of sleep paralysis usually ranges from 14 to 17 years, we studied adolescent subjects with the aim to elicit accurate data about frequency and features of initial sleep paralysis episodes,” noted Dr. Jiménez-Genchi. All participants completed a Sleep Paralysis Questionnaire and the Epworth Sleepiness Scale (ESS). About 90% of the adolescents had heard the expression “A dead body climbed on top of me,” and 26% had reportedly experienced the phenomenon.

The investigators found that 68% of participants had had one to three episodes of sleep paralysis in their lifetime, while 19% had such an experience several times per year. In addition, 6% had an episode once per month, and 3% had several per week. About 24% of females experienced sleep paralysis, compared with 32% of males. ESS scores of participants who had had an event within the previous month were not significantly different from those who did not have a recent event.

Adolescents who had an episode of sleep paralysis experienced a variety of effects—86% were unable to move, 73% were unable to speak, 44% had chest oppression, 47% had a sense of a presence, 29% experienced visual hallucinations, 24% had auditory hallucinations, and 13% had tactile hallucinations. When using a clinical diagnosis of sleep paralysis, the investigators found a prevalence of 29%. “However, only about 50% [of this group] were positive for both the folk and clinical description,” stated Dr. Jiménez-Genchi.

“We speculate that while the folk expression seems to capture all the features of sleep paralysis in an abbreviated term, the clinical description includes just one characteristic—the inability to move—and possibly it becomes unspecific,” Dr. Jiménez-Genchi told Neurology Reviews.

COMPARING ETHNIC GROUPS

The prevalence of sleep paralysis in the Mexican adolescents is lower than rates found in studies of Japanese (39%), Chinese (37%), Korean (34%), and African-American (41%) subjects, according to Dr. Jiménez-Genchi. “However, these investigations were done in young adults or adults, and we studied only adolescents,” he pointed out. “We excluded subjects 18 years and older from the analysis. Nevertheless, if they had been included—they ranged in age from 14 to 22 years—the prevalence increases from 26.4% to 28.7%. In other words, there is a ceiling effect.”

Although the origin of the “A dead body climbed on top of me” expression is unknown, “it has probably been transmitted through oral tradition from one generation to another,” noted Dr. Jiménez-Genchi. “As far as I know, there are no data about the origin of the phrase. Someone asked me, ‘Why a dead body and not a live body?’ Maybe the Mexicans’ death culture is related to the construction of the phrase in combination with some features of the phenomenon, such as the paralysis and the sense of chest oppression. But this is just speculation.”           

NR