But it does explain why the blood slowed dramatically when I went half deaf and fizzy visioned - there wasn't enough blood in the top half of my body.
However, looking up treatment methods had my laughing my ass off - this line in particular: "The cornerstone of treatment is avoidance of triggers known to cause syncope in that person." Uh, well, DUHHH. Not the most helpful bit of advice I ever heard. (And I'm guessing these tablets won't help much.)
With a bit more digging around I now know that lying down and putting my legs up will help reduce this particular side effect of my phobia. Rumour has it that licorice root helps too. Although useful to know, the response is... well, purely a response to emotional stress and not the underlying problem.
I'm not sure how to progress from here, except to get more blood tests I guess, like immersion therapy or something. Oddly, the internet isn't offering many useful suggestions. Any ideas?