SO masturbating in his Sleep

A few times now I have been woken up from my boyfriend tossing himself off him his sleep, I checked and his always definitely asleep, I find it funny because he does all sorts in his sleep, have deep conversations, does a bit of sleep walking and now this. Only thing that annoys me is me getting woken up! A couple of times he wakes up in the morning and find his boxers down to his ankles and can't even remember why and how. Just wondering if anyone else have this happen? 😂