I was going to reply with exactly what Ellie had said about lying dwn while having your blood drawn. Passing out is the bodies way of protecting itself, example, B/P drops, you pass out, now your head is at level with your body, B/P returns to normal.
You'll be fine if you lie dwn.........Dont think too much about it. I know that the Xanax should not affect the results (I'm on a similiar) and have never had a problem but double check w/ the Dr.
Another thing is this....perhaps it helps. Most people who are sensitive and scared of getting blood drawn is due to the fact that you see HOW much blood is coming out into All those lil bottles. Fact is, its such a small amount......my Dr once told me people think it looks like so much, commenting on "oh my, how much are you taking". He says its like a tablespoon, same as menstruation goes, looks a lot more than it really is.
So if it helps any, lie down & keep telling yourself, its not a lot of blood!
Relax, get it done, its vital to your health. You'll do fine.
Good luck, we hope to hear good news!'