I find this very interesting. I get scared in certain situations - I'm OK being on top of a tall building, even looking over the edge - but only if I can't fall. anywhere with no 'safety net' like a cliff or rope bridge does me in. I also get vertigo by proxy - my GF has no fear and will happily stand on the edge of a cliff (she did once at beachy head - looked back to see me lying on the ground 30 feet from the edge pleading with her to get back!!)
In Canada last year we drove up a logging road, about half way along a mile-long stretch we had to stop. I got real vertigo as the sheer drop on my left was too much! Had to reverse down slowly...
The thing I find (and I know this will sound strange) is that I feel unsure that I wont throw myself off. No through any desire to kill myself - but like it is a deeply subconscious urge. I've often wondered if there is some part of the brain that 'remembers' flying at some hugely deep evolutionary level, and it is the instinct of this that we fear, but also compels us to spend time and money learning to do what we love - even if this appears to contradict our responses in other situations. Probably complete bo-lo's, but I like to ponder on these things.
JP