Getting blood taken is horrible. I did it about two years ago and right after it was done, I got a strep test.
Immediately afterwards I was very hot, felt n*, and my head hurt. All I wanted to do was lay down. It was winter and I walked outside without a coat and I wasn't cold. I lied down in the car and about three minutes later I was fine.
Last Apirl they took my blood again after getting a shot and I was fine. Maybe it was the strep test and being nervous that set me off.