Keep a close eye on any changes is the best thing to do. Sometimes there are just too many changes to keep up with what is causing what. Then you just have to make the best judgement, see what happens, and then try again.
Just a quick word on the TMJ. Usually with TMJ is is worse when they move the mouth, there are clicking sounds, and a limited ability to open the mouth. I was actually diagnosed with TMJ but had none of those symptoms. Just a sharp pain that was actually a little in front of the ear over the joint in my jaw. It turned out to be a nerve problem irritated by muscle stress. It was properly diagnosed by my dentist of all people! Rather than surgery, I had a few deep tissue messages and it got better! Doctors, at least here, tend to jump on the TMJ for anything that affects that area of the face when it may be something very different.
The muscle rigidity can be caused by any one of a number of anti psychotics. Neuroleptic malignant syndrome, or NMS is a very dangerous side effect. It is often accompanied by fever, unstable blood pressure, imbalance, and cognitive changes (delirium) along with the rigidity. The good news is, when the medication is stopped and symptoms treated, there is usually a good outcome.
Again... I do hope he will recover to a point that he can go back to close to where he was before