For all who pass out when you have your blood taken, how can you avoid it?
As someone who has drawn too many people to remember, this is my suggestion.
First, if you simply don't like it, please don't add any more drama to the situation than necessary.
But if you have a true aversion to it (I could usually tell because they were the ones who didn't say a word, petrified), please tell your health care worker that you have a history of passing out when your blood is drawn. If a really quiet one didn't tell me, I would ask. If yes, I would lie them down to eliminate the falling on the floor! Then while taking the blood, I would attempt to talk with them about their subject of choice. Most would happily talk to take their minds off of it. A few would remain silent, I would leave them alone, but watch carefully. I never had a fainter faint on me when we took these measures.
Oh yes, and most importantly, don't hold your breath during the procedure!
My personal hall of famer passer-outer? A 250 or so lb man who was doing fine, took a deep breath, snapped the tray that the arm sits on in half and slid to the floor in slow motion. I can still see it! He was fine after a few whiffs of smelling salts.