"I believe these sorts of events are relatively uncommon, although many events, such as hitting or choking and so forth may be going unreported," said Michael Mangan, a psychologist and faculty member at the University of New Hampshire, Durham.
"Violence is reported to occur most often in cases of sleepwalking disorder, REM behavioral disorder and in sleep terror disorder, all of which have a relatively low prevalence of 1-5 percent among adults," said Mangan, who wrote the book "Sleepsex: Uncovered."
Cartwright could also only guess at how common violent parasomnia really is.
"We really don't know," Cartwright said. "The last big survey on sleep-related violence was done in the U.K. on 5,000 people and got a rate of 2.1 percent," she added. "That the rate is escalating is suggested by the number of cases related to the use of the newer sleep meds [such as Ambien and Lunesta, especially if combined with alcohol]."
Schwartzreich said Mark Kaplan was taking an allergy medication at the time but has not heard one way or the other if this could affect his sleep.
Experts say whether an explanation of violent parasomnia and sleepstrangling will hold up in court could actually come down to physical evidence. Sleep experts can already evaluate a person to test for a parasomnia.
"It's certainly possible that his behavior occurred in sleep," Mangan said. "If this is indeed the case, then he would not have been in a state of mind such that he could form the conscious intention to harm her.
"However, to determine the likelihood that this is what actually happened would require an extensive forensic sleep study."