If it is not trauma, then it may be an autoimmune response. We are only guessing without x-ray image, full medical history, etc. Did you use a new toothpaste, oral rinse, whitening or any other mouth products that seemed to irritate? Do you use any cinnamon, herbal, and or naturopathic products? Stress from an overseas trip can throw your immune system off balance. My guess besides trauma is herpetic (viral triggered by stress) or autoimmune response. If the lesion is diagnosed as herpetic, have a doctor/dentist prescribe you Acyclovir. If autoimmune, get Kenalog in Orabase. If unknown and very painful, start with Acyclovir or Valacyclovir (don't use Kenalog if it is viral because it suppresses your immune system to fight off the virus) and if not responding in 3 days, switch to Kenalog and try to identify any source mentioned above and stop using it.
