I got stung on the head once, felt weird and left a message on my own answerphone saying I wouldn't be going out that night!!
I've been stung before and haven't had a reaction, I'm sure it was just because I got stung in the noggin, BUT! like other people have said get yourself checked out by your GP - a severe anaphylactic reaction can be fatal, but something an epipen can remedy. It's certainly worth getting checked, especially being an outdoorsy mountain biker....