About 6.2% of the general population in Germany and Italy has experienced at least one episode of sleep paralysis, with 0.8% experiencing severe episodes (at least one per week). Sleep paralysis is less common than earlier small-sample studies suggested. The condition is often linked to mental disorders; users of anxiolytic medication were nearly five times as likely to report sleep paralysis, even after accounting for mental and sleep disorders. Other predictive factors include automatic behavior, bipolar disorders, physical disease, hypnopompic hallucinations, nonrestorative sleep, and nocturnal leg cramps.
In a representative UK community sample of 4,972 people aged 15-100 interviewed by telephone, 37% reported hypnagogic hallucinations (occurring when falling asleep) and 12.5% reported hypnopompic hallucinations (occurring when waking up). Both types were more common among those with insomnia, excessive daytime sleepiness, or mental disorders. The prevalence of narcolepsy in the UK was 0.04%. Hypnagogic and hypnopompic hallucinations were much more common than expected, far exceeding what narcolepsy alone can explain. Hypnopompic hallucinations may be a better indicator of narcolepsy in people reporting excessive daytime sleepiness.