Depends on where I am. Tall buildings and flying apparatuses are perfectly fine, but I try to avoid getting to the edges of rooftops, some roller coasters, and anywhere else where a single tiny mistake can prove lethal.
Actually it's just a discomfort I think because I love AtmosFEAR and the Ferris Wheel.. it doesn't really matter when there's adrenaline involved I guess ;D
i'm fine in aircraft, tall buildings; hell with those i could stand on the edge and look down with out fear, but oh god i will not go up a ladder that goes higher than the 2nd story.
If i could fly i would be fine.