I first knew that I had an issue with seeing my blood almost 20 years ago when I saw it shooting into a vial when I was getting the bloodwork done before getting married. I was 20 years old and had never had blood drawn before, so I sat there staring directly at the vial as it filled with blood. I quickly felt the room start to spin and like I was going to loose consciousness and fall out of the chair. But I shut my eyes tight and gripped the other handle of the chair to keep myself from tipping over and just forced myself to take deep breaths until my head stopped spinning and I knew I wasn't going to black out. Ever since that episode, I have a policy of never looking when they stick me or when the vial is attached to my arm to collect the blood. I have no problem with getting stuck with needles, just with seeing my blood shooting out. I think it is more the idea of seeing my blood, on which I rely for my very precious life, shooting out into that vial and knowing that if enough of it came out, my life would flow out with it. In your logical mind you know that the nurse would never allow that to happen to you, but I think this is a primal reaction to seeing one's own blood, just an underlying feeling that your blood is supposed to stay in your body and not out, out is bad.
Here's to not picking yourself up off the floor in any doctor's office anytime soon.