<s>[INST] when I sit forward my jaw seems to be sliding forward, like it isn t being held in place by the muscles like it should be. This is a new symptom for me. I normally have a normal bite, but if I sit forward, like looking down at a tablet computer in my lap or sitting at a desk working, my jaw slides forward creating a significant underbite; I noticed this because it causes great pain and headaches.... I don t know what to do? [/INST] Hello, In my opinion, it could be a subluxation of the TMJ disc, so you just need to see a TMJ doctor for a quick reduction that takes a few movements. Until then, open your mouth and measure The height of the mouth opening, it should be 3 fingers. Push your lower jaw backward with your hand towards your neck. This can help reduce your symptoms. Hope I have answered your question. Let me know if I can assist you further. Amman Darragh, Physical Therapist or Physiotherapist </s>