Flu shot

I just returned to my desk from getting a flu shot, downstairs in our company break room. I realize it's a good idea for companies to offer free flu shots to their employees, but I've always found it awkward to sit in a room with co-workers as nurses poke you with needles.

For whatever reason, I didn't get a flu shot for the last few years, so my nurse asked me to "stick around" for 15 minutes afterward in case I exhibited any adverse reactions. Fortunately, I'm not vomiting or anything, but I'm starting to feel a bit warm. Is it psychosomatic? Am I reacting adversely to the vaccination? Do I have swine flu? Am I dying?!