Even stranger than sleep-eating is sleep sex, or sexsomnia. First described in a 1996 case study of seven individuals, sleep sex can range from annoying (loud sexual moans) to dangerous (self-injurious masturbation) to criminal (sexual assault or rape). In at least five controversial cases, men have been acquitted of sexual assault by arguing that they were asleep during the attack.
Most research on sexsomnia have involved small case studies. The largest study, an Internet survey of 219 people who said they experienced sleep sex, is limited because it relied on self-reports. Even so, that study, which was published in 2007 in the journal Social Psychiatry and Psychiatric Epidemiology, suggested that sleep deprivation, stress, alcohol, drugs and physical contact with a bed partner play a role. But no one knows why some people respond to these triggers with sexual behavior.