Gosh, that sounds painful. Clearly something is going on! Have you been to the doctor as of yet? So, you are having pain on ONE side of your jaw only and it's new. You'd say it is at the hinge area of the joint? That area an have moved out of alignment causing the pain. Obviously that can happen manually (like a punch) but the disc there can also erode. You actually can have cartilage issues in the jaw and arthritis? You don't mention your age. Did you have a previous jaw injury? Jaw pain is also on the list for a symptom of a cardiac event. Any possibility of that? Stress and posture issues can aggravate it.
Have you tried any nsaids like ibuprofen or motrin for it? That would reduce any internal immflamation and acts as a pain reliever. Does it do anything for you? There are other meds they might use but this is where I'd go first for sure. Then if that doesn't work, they do have other things you can try . . . even physical therapy! An oral splint. Etc. Surgery is a last option in my opinion.
Anyway, those are some ideas for you to start with. Tell me what you think and how you are.
Ya, it does. Any chance it follows your being stressed and grinding your jaw for a couple of days prior to it happening?