A 24-year-old man whose girlfriend accused him of sexually assaulting her during the night told doctors he had no memory of it. When sleep specialists in Paris recorded him overnight on infrared video, they confirmed a rare sleep disorder and noticed an odd detail about which hand he used.
During partial awakenings from sleep, the man repeatedly slid his left hand into his pants and touched his genitals. Twice, he made movements suggestive of masturbation, always with his left hand. Yet he later told doctors that when he is awake, he always uses his right.
The case, published online Feb. 2 in Sleep Medicine by clinicians at the sleep clinic of Pitié-Salpêtrière Hospital in Paris, confirmed a diagnosis of sexsomnia. It also adds weight to an emerging idea that sexual behavior during sleep may be driven by different brain circuits than deliberate, waking movement.
Six Years of Nights He Could Not Remember
The man was referred by his primary care doctor for excessive daytime sleepiness. He scored 16 out of 24 on a standard sleepiness scale and needed two to three naps a day.
He also reported six years of sexual behaviors during sleep that he could not remember, occurring once or twice a week, usually early in the night. They included masturbation, fondling, and one assault on his girlfriend, who filed a police complaint. She later withdrew it.
He talked in his sleep and had sleepwalked as a child, which the authors identified as a predisposing factor. He did not use any drugs or other substances.
Sexsomnia is a non-REM parasomnia, a disorder in which a person partially wakes from sleep in a confused state and carries out complex behavior without awareness. The authors noted that video examples are rare. The stakes can be high: in a 2017 study of 17 patients with sexsomnia, researchers at the same Paris hospital found that the behaviors had led to six sexual assaults.
What the Cameras Recorded
Over two consecutive nights of video polysomnography, a test that tracks brain waves, eye movements, muscle activity, and breathing, doctors found mild or no sleep apnea. They also found repeated arousals from the deepest stage of non-REM sleep, at rates above normal reference values.
During arousals from the N2 and N3 stages of non-REM sleep, and from REM sleep, he placed his left hand inside his pants and touched his genitals on both nights. The masturbation-like movements arose from N2 and N3 sleep. His eyes stayed closed, and at no point, even in the laboratory, did he recall any behavior or mental activity during sleep.
A standard handedness questionnaire produced a less clear-cut picture. His score of 25 out of 100 indicated functional ambidexterity with a preference for the right hand, and his account of using only his right hand for the behavior while awake came from his own report.
Why the Other Hand Could Matter
The Paris team linked the case to a 2025 series in the Journal of Clinical Sleep Medicine, in which doctors at UCLA, the University of São Paulo, and the University of Minnesota described seven patients whose sleep-related masturbation mostly or entirely involved the left hand. Six of those patients were right-handed, and one was ambidextrous.
Those researchers speculated that such behaviors originate in central pattern generators, networks in the brainstem and spinal cord, rather than in the cerebral cortex, which plans voluntary movement. Patients' lack of memory for the episodes, they argued, further suggests the cortex is not in control.
In deliberate movement, each side of the brain controls the opposite side of the body. The Paris authors wondered whether sleep behaviors might instead travel along a direct rather than a crossed motor pathway, and they said their case supports the earlier finding. Both groups presented these ideas as hypotheses, not established mechanisms.
Video evidence of this behavior is still scarce. A 2016 report in Sleep Science described what its authors called the first video-documented case of sleep masturbation in a male, a 20-year-old soldier whose episodes were triggered by military shift work.
The Paris authors also stressed the legal stakes, writing that "visible masturbation in video-polysomnography has significant legal relevance."
A Treatment That Backfired
There is no consensus treatment for sexsomnia. Doctors advised the man to improve his sleep habits and prescribed gabapentin, 300 milligrams an hour before bed. He said he felt less sleepy and more attentive, but he could not judge his sexsomnia because he slept alone.
Seven months later, a repeat sleep study showed that his apnea-hypopnea index, a measure of breathing interruptions during sleep, had climbed to 21.8, and the masturbation continued. Gabapentin has previously been reported to worsen sleep apnea, the authors noted, including in a randomized trial in older men. Clonazepam, another drug commonly used for parasomnias, can do the same.
Doctors switched him to paroxetine, 10 milligrams. On his next sleep study, the index fell to 10 per hour, and the deep-sleep arousals were gone. That study had no video, however, and he still slept alone, so the drug's effect on his sexsomnia remains unknown.
The report describes a single patient, and its conclusions are limited accordingly. People who are told they behave unusually during sleep, or who have nighttime episodes they cannot remember, should talk with a sleep specialist and should not start, stop, or change medications on their own.
Key Questions Answered
What is sexsomnia?
It is a non-REM parasomnia in which people carry out sexual behaviors during confused partial awakenings from sleep, usually with no memory afterward.
What was unusual about this case?
On video, the man used his left hand during sleep episodes, while he reported always using his right hand for the same behavior when awake.
Why might someone use the other hand during sleep?
Researchers have proposed that these behaviors are generated by networks in the brainstem and spinal cord rather than the cortex. The idea has not been proven.
How is sexsomnia diagnosed?
Specialists rely on a detailed sleep history and video polysomnography, an overnight test that records brain activity, breathing, muscle activity, and behavior.
Does medication help?
No treatment is established. In this case, gabapentin did not stop the episodes and worsened sleep apnea, and paroxetine's effect on sexsomnia could not be judged.
