How do you deal with TMJ (temporomandibular disorders) if stressed?

Deal with stress! Tmj problems are often made worse by stress. The answer is to deal with the underlying stressful problem. Everyone has stress, and different people deal with stress in different ways. Some people internalize it, and express it by grinding their teeth (bruxism). This makes TMJ problem worse. Usually, simply being aware of it will help you stop doing it. Otherwise, see a specialist for evaluation.
SEE your dentist. Your dentist can make a anti-bruxism appliance or "night guard" which helps many patients. When you are stressed you tend to clench or grind your teeth, or both, which is harmful to the tmj. This appliance will relieve pressure on the joints and you will feel noticeable relief. Many chiropractors can do adjustments that can relieve your symptoms.
Pain Psychologist. Behavioral techniques like postural training, cognitive behavioral therapy biofeedback and proprioceptive retraining. Pain psychologist is always a member of the Orofacial Pain team. See Orofacial Pain specialist for consultation and conservative treatment.
Learn about TMJ. Learn everything you can about TMJ to help you manage it. Knowledge is power! TMD, TMJ, Complex. TMD mostly managed by dental TMJ specialists. TMJ experts are most commonly, oral surgeons,
MANY MODALITIES. Multiple treatment forms ranging from stress relief treatment to splint treatment.
Depends. The stress needs to be under control first. True, if the tmj/tmd is leading to your stress, then you should see a dentist/tmj specialist first. It can be a double edged sword in that one can cause the other. Best if can deal with both at the same time...Stress management, etc. Combination of physical and emotional therapy may be needed.