The prevalence of sleep paralysis among Canadian and Japanese college students

Although sleep paralysis had been treated as one of the symptoms of narcolepsy, recently it has become recognized as occurring frequently in normal individuals. However among the few published studies that have examined sleep paralysis, there are great discrepancies in its reported prevalence. These discrepancies could be attributed to differences in survey methods, to the description of the symptom employed in each study, or to the race or culture of the research participants. We administered a questionnaire, with equivalent Japanese and English forms, to 86 Canadian and 149 Japanese university students. Although the reported prevalence of sleep paralysis was almost the same (Canada: 41.9%, Japan: 38.9%), the characterization of the phenomenon differed greatly between the two samples. Over 55% of the Canadian and only about 15% of the Japanese students regarded the experience as 'a kind of dream.' This difference may be one of the reasons for the varying prevalence noted in previous studies. Although many Japanese students (40.5%) and a very small number of Canadians (3.5%) usually prefer the supine position while sleeping, the majority of both groups (Canada: 57.9%, Japan: 83.8%) reported that, during the episodes of sleep paralysis, they found themselves in the supine position.