I can report similar to above posters - terrified of anything above the ground floor windows on a ladder yet will sit with legs out of a Helo all day quite comfortably. Some very interesting explainations so far.
On an aside, when mini was young and in the military he wanted to try out for a shady unit, decided the "regular" elite was not for him as they did the parachute, abseil thing so he joined the underwater mob.
Nine months of hell was tackled only to find that the final day of selection involved a suprise jump off a bridge (20M) into a lake. It probably only took two seconds to hit the water but it felt like a lifetime. I remember thinking about the irony of it on the way down.
15 odd years on as a civvy I still dive, and I have no problems with depths of 60M +, guess I'm not a bathywhatever?