"Stuck" or "Lock" The major sign is jaw that is locked in position or difficult to open. TMJ dysfunction is a group of conditions that can cause joint lock and visit to your dentist is warranted.
TMJ. You are probably referring to a jaw joint (TMJ) problem and not true lockjaw related to a tetanus infection (http://en.wikipedia.org/wiki/Tetanus). The TMJ problem you are describing starts with clicking of the jaw joint, often joint pain and limited oral opening. Bruxism makes it worse. If you have suck a profile, see a TMJ expert.
Clicking in TMJ . If you damage your jaw in an accident, increase grinding due to stress, bad habit of opening mouth in size too much that causes dislocation of disc in TMJ through time and then clicking sound, rare causes neurological problem. There are many factors that needs to be check before diagnosing. So, if you think you are developing lockjaw, you should see a prosthodontist or gnathologist (tmj).