I know it's not much help, but I had numbness of my lower right lip a few weeks back. It lasted about a week. I have Harlequin or Incomplete Horner Syndrome depending on the Doc you talk to. (lack of sweating or flushing on half the face). I also have worse TMJ on that side. I assumed the numbness was due to one or the other. I've been to the Doc since then and he didn't seem to worry about it. Do you also have one of these issues?