I agree, drink as much as you can before and after. It is lack of volume in your system that makes you faint. I have fainted twice after giving blood and neither time was it because I am squeamish (I am an ICU nurse). I was just busy and didn't take in the fluids that I should have. That doesn't stop me though, I still try to give whenever I can. The two incidents were 10 years apart so it isn't like it is a common problem for me.