Puppetmaster, you are wrong....
This happened to my dad when he was giving a speech. He was very nervous but at the time didn't recognize it as anxiety. He had taken half a muscle relaxer to help calm his nerves. This was not a big deal for him in the past, as he had not had problems with the muscle relaxer, for non-anxiety related issues. Anyway, he was doing his speech, ironically on the effects of stress on the body and basically keeled forward face first onto the ground. He was in the hospital for several days as a bunch of tests were run. Well the doctors concluded he passed out from an anxiety attack. This was only confirmed days later and his newfound anxiety kicked in full force. He was plagued with it for several years. The doctors told him had a vasovagal response, which is brought on by stress, trauma, anxiety, etc., and when this happens, the blood pressure drops too low and voila, you can pass out.
If you don't believe me, google it and google anxiety and passing out. I know this stuff because of my dad and also because I have had a couple of vasovagal events myself. I also have had severe anxiety in the past. So I am sorry but you are wrong.