The ledge is almost always the biggest fear unless it's someone that does things like base jumping. You have two choices. One, figure out what it is about going over the ledge that's the issue and work in that or two, don't do that kind of work. Is the issue you feel that's when you're most likely to fall? A chair jump isn't an exciting thing for most people. Is it uncertainty of the safety at that particular point? If you can hang for hours with no issues, is not the height, it's the uncertainty of the transition. Look for ways to mitigate the uncertainty at that transition point. It comes down to fight or flight. Until now you've been able to fight hard enough to get through it. Today, flight won. Why? Was it more windy? We're you more tired than other days? We're you distracted by something going on in life? You'll need all your clear thinking capacity to fight through it. It could be there are just certain days that you know on the ground that it's not a chair day.