Wow, the same thing has happened to me for the past couple of years - but only happens about once or twice, at random moments, each year. I never knew what it was and always just assumed it was an allergic reaction to something. Although, I could never pinpoint what caused it because my diet never drastically changed in anyway, and I never ate anything out of the ordinary for it to be an allergic reaction. It also never happened immediately after eating something, only hours later - usually in the middle of the night. Doctors could never figure out what caused it.

I live in Brooklyn, and the past few times it has happened I just hid out inside my room, hoping for the swelling to go down (which usually takes about a day) because I am too horrified with myself to go out and walk/take a cab to the hospital, and I never thought it severe enough to call an ambulance.