The phenomenon, called sexsomnia, is a form of parasomnia, a disorder in which people who are asleep but in a state of semi-arousal engage in behaviors they are not conscious of. Sexsomnia is defined by the International Classification of Sleep Disorders and may take place during a sleepwalking episode.

It's hard to believe, but sexsomnia — making advances and performing sexual acts while in the grip of sleep — appears to be more common than once thought. Researchers have found almost 8 per cent of patients at a Toronto sleep clinic reported they initiated or engaged in sexual activity with a partner while asleep. The prevalence of sexsomnia was almost three times higher in men (11 per cent) than in women (4 per cent).

OBJECTIVE: To describe a distinct parasomnia involving sexual behaviour, which we have named sexsomnia. … Sexsomnia has some distinct features that separate it from sleepwalking.