I have TMJ. I find myself clenching and grinding my teeth even when I think I'm relaxed. Some who have TMJ, can get a bite splint from their dentist to wear during the night. They just take a mold of your two front teeth and two bottom teeth. Then when it's time to go to bed, you just pop it in.
I had a bite splint, but I lost it since I got it. My makeup bag got stolen at a hotel and it had that in there too. :(
However, when I had my bite splint, I did notice a difference in my TMJ. My jaw felt more aligned and did not "pop" as much. (It actually popped this morning and still feels a little out of place)
The bite splint also helped to lessen my habit of grinding my teeth during the day. If people have sever TMJ, I definitely recommended trying one of this!
Otherwise, just consciously try and relax your jaw. I am right now and it feels a little better. :) Sometimes if I massage both sides of the jaw, it helps me to relax the muscles even more.