Current Psychiatry has an article this month on "sexsomnia":
Sexual behavior during sleep (SBS)—or “sexsomnia” ...is more than a sensational defense for a high-profile court case. Sleep physicians are finding that sexual behaviors during sleep are real and more common than previously thought. Although SBS cases sound psychological in origin, it appears that the problem lies in the brain itself.
SBS can cause great distress to its initiators and recipients but often goes unreported and untreated because of embarrassment about seeking help. Among patients who report their symptoms, many say they experienced SBS 10 to 15 years before seeking help. SBS not only disrupts sleep but can damage relationships and lead to allegations of sexual assault and rape.
I have had only one case of this in my sleep practice- a woman with masturbatory behavior during sleep. She failed all the standard treatments- benzodiazepines, tricyclic antidepressants, and anticonvulsants. Her polysomnogram and EEG were essentially negative. I ended up referring to the local university sleep center for a second opionion. She didn't keep her follow up appt with me and I have no idea what happened to her.