We're going through the same thing at the moment. DS is 6 months old and has been able to roll over for ages, but about 2 weeks ago I put him on his tummy and he spotted the cat and it was like a lightbulb went on in his head! He loves the cat and obviously realised that if he could co-ordinate the rolling onto his tummy and the leg wriggling, he might stand a chance of getting to her! He's so caught up in this new skill that he is practicing any minute he can get!
We were lucky enough to be bought a "CCTV" style monitor for LO's room and DH and I can see what he's up to. DS only ever cries out when he gets an arm stuck underneath him and can't physically roll back. (We're working on practicing this during the day but I guess it's a strength issue.) I've just been placing him back on his side and leaving the room and this seems to be ok for our LO but he's generally a good sleeper.
You could also try using bolsters - we've been using rolled up blankets or towels to support DS at night time as he loves to sleep on his side and he also likes to snuggle into something. Of course he's now figured out how to wriggle up the cot past them, but it does the trick some nights!
Hope you get some sleep back soon!