If you think it might be TMJ or something, I'd go to the dentist, casually ask them about it (while I got my teeth cleaned :-)

There's all kinds of nerves in there, maybe your bite is a bite is a bit off or a wisdom tooth or something is sitting on somthing, etc. I'd check with a dentist and then, depending on what they said, pursue it with my GP or get a consult with a neurologist. Doesn't sound like something you would die from though?

"Girl dies from tightening of the cheek! Who knew that could happen????"