I had a similar experience a few years ago. I was going down a hill at about 40 mph (about 65 kph) when a bee hit me just above the lip and stung me from the impact. My lip was a bit swollen, but I figured it was normal. The next day, I could tell something was wrong as soon as I woke up. The area above my lip was swollen, and it continued to do so through out that day. The swelling spread up as far as my eye, and started down towards my throat, so I went to the ER. This was almost 24 hours after the initial impact. Benadryl and steroids got it under control. Now I carry a bee sting kit in case I get stung again.

Jonathan Vaughters had to drop out of the Tour de France a few years ago because his face was stung by a bee and he swelled up so badly that he couldn't see out of one eye. The condition could have been easily remedied. However, he was afraid to do so because if he had been tested for drugs afterwards, he would have come back positive. It's quite a shame, because these drugs would have been obviously for medicinal purposes, rather than performance enhancing.