You can't really know it will affect you until you do it so....now you know! I have to have my blood drawn (usually 4 vials) at least once every 3 months to check kidney and liver function and it's never bothered me but I know some people feel sick just from LOOKING at a needle. I agree to just eat better, preferably carbs or some other complex sugars. Usually they give you chocolate afterwards? I've never seen one that gives pretzels. If you still want to but don't want this feelings again maybe take some fruit or juice with you for right afterwards.

Unfortunately I can't give blood :-/ Stupid epilepsy. I've always wanted to though. I'm glad you're doing it!