This feeling is commonly related to jaw muscle tightness, teeth clenching/grinding (especially during sleep), or a temporomandibular joint (TMJ) issue. Stress and night-time grinding can make the jaw feel “locked” or very tight when trying to open the mouth. In most cases it is not dangerous, but it should not be ignored if it is happening repeatedly.
Next Steps
If you also notice jaw pain, clicking sounds, headaches, ear pain, difficulty chewing, or limited mouth opening, it would be best to get a dental evaluation done. A clinical examination can help check your jaw joint, bite, and signs of night grinding.
Health Tips
For now, try to avoid chewing gum, very hard foods, and excessive jaw movement. Warm compresses over the jaw area and gentle jaw relaxation exercises may help. Also try to reduce stress and avoid clenching your teeth during the day.