O que eu encontrei (de esta fonte original):
The whole concept of disease or illness is often related to emotions which have been repressed. When a person holds in anger, that angry energy has to go somewhere. Some people hold it in their jaw, others in their chest and some in their stomach. Angry energy can actually be held anywhere and everywhere in the body. This energy, if not released, then does violence to the body itself, in the form of disease. So the person that holds in their feelings and does not say what needs to be said, may experience tension in the jaw which can result in TMJ or grinding of the teeth.
Você vê isso em outros filmes de terror como Secret Window . O personagem principal lá também apresenta sintomas da ATM.