It happens to me just about every single time I have to have blood drawn.
I now insist on lying down, and sometimes I still faint. It is a bit better if I am talking, or have a small piece of candy tucked in the side of my mouth, and the skill of the phlebotemist definitely makes a big difference.
I once had a tech tell me that no one ever fainted when he took blood and that I would be fine. Well, I sat in the chair he pointed to and he began. The next thing I knew I was on the floor, with my arm above my head with a very very pale tech finishing up the blood draw.
The doctor that I see now is wonderful and she has had the best luck with getting blood without me fainting. We had one time when she couldn't find a vein....that is the other problem I have......and needed to stick me over and over. Needless to say I was getting really anxious. She offered to come to my house later that evening to do the draw!!!! That was one of the few times that I made it all the way through a blood draw without having a problem.
For me, it is stress and plain old fear....and my blood pressure dropping really fast. It is both strange and really annoying when it happens. Of course I have also fainted at the mere sight and thought of blood and pain....movies, ER on TV, conversations about gross things, pictures of icky surgical scars, and actual scars and stitches. What is strange is that if I am the only person in an emergency, and a person's life depends on me....I can provide care. As soon as someone else arrives on the scene I have to so and lie down.....and typically faint.
I wish it were different, but I have been living with this since the first time I fainted at age 5.
Linda