The phenomenon arises just prior to falling asleep or on awakening (ASDA, 1990;
Takeuchi, Fukuda, Sasaki, Inugami, & Murphy, 2002) and is often accompanied by hypnagogic (sleep-onset) or hypnopompic (sleep-offset) hallucinations. Sleep paralysis can also affect individuals without excessive daytime sleepiness or cataplexy—that is, without a diagnosis of narcolepsy—and is referred to in those cases as isolated sleep paralysis (ISP;
ASDA, 1990;
Fukuda, 1994;
Hishikawa & Shimizu, 1995;
Takeuchi, Miyasita, Sasaki, Inugami, & Fukuda, 1992)