100 feet off the ground? You think that's a lot?
Try the Peak-to-Peak gondola at Whistler-Blackcomb. It is over 1,500 feet off the ground when it crosses the lowest point between the two mountains. And just in case that's not enough, two of the gondola cars have see-through floors...
I have some measure of acrophobia, but chair lifts don't bother me, for some reason. It can get a little exciting when the lift undergoes an abrupt stop when the chair is in the middle of an especially long span between towers. The chair can move up and down 5 or 6 feet - or it feels like it, anyway.
What freaks me out is fog, especially if I'm not familiar with the mountain. I get very tentative.
I also get tentative when skiing out of bounds in places with which I'm not familiar. If I can't see over the next grade break, I tend to get very cautious. When I have such a reaction, I don't ski well, because I'm moving back toward my heals.
The first step, then, is to figure out what you're doing different when you see a run or a line that you find uncomfortable. Until you do that, you don't know what changes to make to be more effective in particularly challenging terrain.