Hi MLC - I have the same problem. When my dd was 8 weeks old, she rolled over once while she was trying to fall asleep. She is also a stomach sleeper so she rolls from her stomach to her back, then gets stuck. It only happened once until 2 days ago. Now, she is doing it more often - she is 11 wo. She will either do it when she is trying to fall asleep or when she wakes up and is trying to go back to sleep. She rolls from her stomach to her back, gets startled/scared, then starts crying.
I have a video monitor so I can see what happened, and I go and roll her back over. If I don't, she won't stop crying. If you lo doesn't cry, you can try to leave him/her to fall back to sleep. Otherwise I would roll him/her back over.
I'll keep you posted on what happens with my dd and maybe I can give you more advice.