What's weird is how everyone reacts differently. Someone talked about spinning out in a car; once, my girlfriend was driving, in the winter, and we tried to pass someone on the freeway, going near freeway speeds. The roads were icy, and we spun around multiple times, and ended up coming to a stop on the other side of the freeway facing oncoming traffic. Throughout the entire episode, I remember only thinking, "Ok, this is happening." I wasn't afraid, my heart rate was normal, I was completely calm. I think I may have put my hand on the dashboard, as if that'd do anything. I think, for me, it was the utter inability to do anything about the situation that made me calm. I've lost control on ice while I've been driving, and that's nerve-wracking. But that one time was the worst, and yet I had no fear. It's really strange, isn't it?
So, my answer is being up on the town hall tower in Rothenburg, Germany.
I know I'm acrophobic, but not pathologically, but I figured I'd be a little scared and that would be it, and I wanted to do it. So we climb about 800 floors of stairs and crawl through this little submarine-like hatch onto a mayor walkway around the tower literally wide enough for one person, as long as they're not too fat. The railing is a metal bar about waist-high, and I am not joking, you didn't have enough room to turn around. So you shuffle around the entire spire - there's just a column behind you - until you make the circuit and can climb back in the man-hole. It was not great; I was already anxious, except that after I got out, people just kept coming out of the hole. It was literally impossible to go back - you had to make the circuit, and there were people on both sides of you. You shuffled as fast as everyone else was, which was slow, because you'd stop when someone would finish and climb back in the hole.
I was about three people out of the hole, and thinking about the warning sign about the walkway being rated for only 4 people at a time, and how by my count there were at least a dozen, and I panicked. It was one of two or three times in my life when I felt like my brain had run off and was doing its own thing, and I had no control. I didn't make a scene, but internally, I was completely terrified, and probably wouldn't have been able to move if I hadn't been part of a press of people on both sides inexorably shifting around the walkway. I don't think that utter loss of any rational control can be adequately described unless you've experienced it.
The view was, apparently, beautiful, but I have no memory of it; all I remember is that it took 6 hours and all I could think of the entire time was getting back inside.