I think my worst episode to date was on a walking trip in Iceland with RB67 over shoulder. Came up to a horrifically narrow ledge going around a corner with about a 600 foot drop into the bottom of the valley. On the outward trip I coped because I couldn't actually see around the corner how far I had to go - on the way back though I knew exactly how far it was going to take me and wound up having a full blown panic attack, with me on the ground clinging onto the Earth for dear life.
To add insult to injury, I later saw a bunch of kids on a pony treck succesfully navigating the same ledge on horseback. Sigh.