If you were sleeping with your window open, my best guess is a mosquito -- and he brought friends!
I am allergic to them. I have had some swell up like golfballs. Benadryl and an analgesic spray clear it up.
Several years ago, there apparently was one in my car. It was summer, so I'd have sandals on and I'd go to the store or go grab a bite to eat and by the time I came home, I'd have 10-12 bites on my feet. (I think it was living on the driver's side floor.
) This went on for months even though I cleaned and even put bug spray there!