Clinical features of isolated sleep paralysis.

Objective: Isolated sleep paralysis (ISP) is a relatively common parasomnia often accompanied by fear and distress. However, little is known about the range and relative severities of typical ISP symptoms and accompanying hallucinations. Furthermore, there have been inconsistent findings with regard to demographic differences in ISP. PATIENTS/METHOD In sum, 185 individuals with ISP (and 322 controls) were assessed for 27 symptoms and hallucinations using a clinical interview and trained diagnosticians. Insomnia symptoms were also assessed.

Results: Rates of ISP did not differ according to gender or ethnic minority status, but higher levels of insomnia were associated with episodes. The participants with ISP reported a mean of 7.73 symptoms beyond atonia. Hallucinations of the presence of others were relatively common. Specifically, 57.84% of the sample sensed a presence in the room with them during ISP, and the majority believed it to be a non-human presence. In addition, 21.62% of the sample experienced visual hallucinations of others, with the majority perceiving strangers as opposed to known individuals. A panoply of supernatural/paranormal entities were reported by the 24.32% of participants who hallucinated non-human beings. A minority of individuals with ISP experienced clinically-significant distress (10.27%) and/or impairment (7.57%) as a result of episodes.

Conclusion: ISP episodes were complex and often multisensorial experiences, and the majority of assessed symptoms were associated with clinically-significant levels of fear/distress. Vivid hallucinations of other people and entities were common as well, and it is recommended that ISP be assessed when patients report seemingly anomalous experiences.