There is the fear of heights and the fear of falling. It helps to try to figure out which you might be triggered by in order to help yourself get thru it. I can stand high on top of mountains and building will sturdy railings. However, anything that I might perceive as unsteady or dangerous, even if only a few feet off of the ground will make me freeze in my steps and panic ( a ladder, a metal bridge with holes in the surface, along a steep cliff, a shaky bridge, a theme park ride that seats you with feet hanging , etc...) If I feel I am secure on my feet, and not at a danger of falling off the side of anywhere, the height does not matter. Walking with poles to feel steady and not close to any any edges helps. The key is convincing yourself that you are grounded. Since you mentioned no issue with roller coasters, consider the fear of falling rather than the fear of heights...you would be seated on the coaster and securely buckled in. Just worth a bit more exploring...it might help you get some resolve. Good luck!