Because the phenomenon is most often seen in childhood or adolescence, Dr. Jimenez-Genchi and colleagues interviewed 230 students from three high schools in Mexico City. "We were surprised to find that most students (90%) had at least heard of the phenomenon," he said.
The characteristics of the "a dead body climbed on top of me" experience "suggest that it is identical to sleep paralysis," Dr. Jimenez-Genchi said.
He noted that not all people experience the phenomenon in the same way. In the vast majority of the cases, the students said they can't move (85.5%); there was an inability to speak in 72.6% of the events; chest oppression was felt 43.5% of the time; and there was a sense of a presence in 46.8% of cases.
Hallucinations were also common: visual hallucinations were reported in 29% of the events, audible hallucinations in 24.2%, and tactile hallucinations in 12.9%.