Fortunately, there are no reports (yet) of people walking out the door and looking for sex. Among 832 people surveyed at a sleep disorder clinic, so not the general population, 7.6 percent had sexomnia or "sleep sex" with partners already in their beds. More often men than women, sexomniacs don't remember having sex, and their partners often don't realize they're asleep.
It affects people the same way other sleep disorders do, with fatigue and moodiness being the most common complaints. Too bad sleep sex doesn't have the same effect as awake sex — maybe some people would get some sleep.