For future reference, now that you know it was an allergic reaction, if you do not have high blood pressure (because if you do, this spikes it higher, which isn't good), take Benadryl in pill form immediately if it ever happens again. It's so connected to a doctor's arsenal for allergic reaction, doctors actually swap my skin with it in liquid form, before swabbing my skin with an antiseptic before operating on me or giving me a shot. I'm allergic to clams, but one of the things in the antiseptic doctors use comes from shellfish of some kind and they do that to protect me from getting an allergic reaction.
Warning though. If you don't use it regularly, Benadryl will make you fall asleep. The firs time the doctor swabbed me was to give me a shot in my back. I wasn't supposed to fall asleep because of the shot, but I fell asleep so quickly because of the Benedryl that I don't remember the shot itself. And, although I was able to get in the car so hubby could take me home, I then slept for 12 hours.
Allergies can hit me pretty bad, so I have Benadryl around my house like some folks have epipens.