I'm not too comfortable with unrestrained heights - like the tops of tall ladders. I think it's the bouncing / swaying that does it.
I don't usually have a problem with cliffs, high buildings etc. - unless you count wanting to toss myself off. Perhaps I should re-phrase that
Never had a problem in an aeroplane or glider (sitting) or balloon (standing).
Interestingly I was cutting down a 35-foot birch tree in my garden last week, and had to climb to about 25 feet AGL and then use a saw to lop off branches - now THAT was scary! No rope - I thought I would be better off falling than accidentally hanging myself (some of you may disagree!).
SD