I did an obstacle course mud run a few months back and at least 4 of the obstacles were climbing up something about 15 feet high, hoisting yourself over the top, and climbing back down the other side. One was a rock wall, one was an A frame wooden ladder, one a rope net ladder one a combination of two of those. The first one (the rock wall) I managed to climb up and then - for lack of better words - freaked the "f" out - and I am probably understating it. I froze. I couldn't move up or down. My friend had to yell in my face to make eye contact with her and talk me down. I skipped the other obstacles because I started shaking just looking at them. If I were on the scaffold I would have passed out. That's part of the reason I can't do big giant coasters - fear of getting stuck.