Yup, classic case of TMJ. Try sleeping with a nightguard, you can buy one at any pharmacy. You may want to see your dentist. I had it bad where it would slip, lock, then I'd have to make a concerted effort to crack it open again. Ended up having orthoscopic surgery and it made a huge difference, no more cracking/locking, but I still sleep with a nightguard. This is the one I use... got it at Walgreens.
