Nightmares and sleep paralysis among the general Japanese population: a nationwide representative survey

The objective of this study was to determine the prevalence of nightmares and sleep paralysis and their associated factors in the general population in Japan. This study was designed as a cross-sectional sampling survey conducted in November 2007. Subjects were selected randomly from among 300 districts throughout Japan. Data from 8099 people (3748 men and 4351 women) were used. Participants completed a self-reported questionnaire on the frequency of nightmares and sleep paralysis in the previous month. In the total sample, the prevalence (95% confidence interval) of nightmares and sleep paralysis was 3.0% (2.6-3.4%) and 2.4% (2.1-2.8%). As for nightmares, multiple logistic analyses revealed that long sleep duration, use of hypnotic medication, difficulty initiating sleep, difficulty maintaining sleep, early morning awakening, excessive daytime sleepiness, and distress had higher odds ratios. As for sleep paralysis, younger age, smoking, difficulty maintaining sleep, and distress had higher odds ratios. This study revealed the prevalence of nightmares and sleep paralysis among the general Japanese population. The results indicate that nightmares and sleep paralysis are induced by high levels of stress and insomnia symptoms in Japanese adults. Therefore, adequate stress-coping skills, sleep education to raise awareness of the importance of maintaining an appropriate circadian rhythm, and effective treatments for insomnia are required.