Out of curiosity, was it also a fasting blood draw? Worst reaction I had was when I stupidly did one of those at like 11:30 a.m. So I already had low blood sugar (and not my usual caffeine) and was feeling lightheaded from that, then had blood drawn. It was right before the doctor saw me, and I had to excuse myself to the bathroom for a couple minutes because I felt so sick that I couldn't really talk to her (I think I lied and said I had to pee). So now, fasting blood draws are much earlier!

I also read this trick online, where if you tense up your muscles in your legs, butt, and non-blood-draw arm, it can help keep up your blood pressure. Seemed to help the last time, though I was afraid the nurse would have asked me what I was doing!