TMJ can definitely be scary stuff, but it's not a brain tumor either.
What I do:
- I got one of those microwave heating bags (mine's in the shape of a sheep), which tends to be kind of damp when I microwave it. So I hold that to my jaw (lasts longer than a washcloth), or even fall asleep resting my head on it (though you do need to make sure it's not too warm if you're going to do that). It helps more than anything else.
- Set a jaw-stretch timer to go off every fifteen or ten minutes. It can be a little annoying, but if it's just a pop-up on your computer or a quiet buzz from your phone it's not too bad. Every time it goes off, stretch your jaw open, let it hang loose, and gently move it from side to side. Every time you catch yourself holding your mouth closed, open it a little. My mouth gets kind of dry, but then I just drink more water, which is a good thing.
- Get someone to massage your shoulders/neck. My flatmate usually does it for me, but getting a professional to do it (especially if they're familiar with TMJ) can be a huge relief.
- Dilute a natural muscle rub in some lotion and then rub a little bit around the hinge of your jaw.