I cannot stand heights. Never have. As a result my wife is the person of choice to deal with anything higher than I can reach and thus needs the use of steps or ladder.
But in my case I am certain it is a fear of falling. So it never bothers me so long as I am strapped in. I did not fancy the London Eye but went and had no problem - hence I agree with those who talk about the magical (illogical) powers of a few millimetres of Perspex or metal.
Just once, literally once, in an open cockpit glider at the top of a winch launch I happened to be able to look down the cable all the way down to the ground and had a sense of being a long way up which I certainly did not enjoy. It was instantly fixed by looking away from the cable.