sounds to me like he has that desease that makes people blurt out curse words uncontrolably at times.
he obviously doesnt do it all the time so he must be on medication for it and my guess is the medicine wheres off around that time while hes asleep and he wakes to take his medicine to go back to sleep.
he may not even realise hes doing it in which case telling him can help him inform his doctor to adjust his medication.
just tell him you heard some hollering from his place and ask if he was ok, that way its up to him if he tells you anything or not.
either way he gets the message that he is having "episodes" in his sleep
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