Something like this has happened to me in the past. If I am having sex with my partner and we fall asleep, sometimes I will wake up 1 to 3 hours later and not realize that we fell asleep, and try to resume relations. This is our in the context of a relationship, and in each it’s been understood that this would not disturb my partner. So, it hasn’t been a problem. Now, if I fell asleep alongside someone with whom I was not just having intercourse (or especially never had done so) and did that, I could see how it would be a problem.