I think it differs greatly from person to person what categories of things that affects you, though.
I'm like GP in that there are many mundane thing that are far more outside my comfort zone than "extraordinary things".
E.g. starting a social conversation with a stranger for any reason takes a lot for me. I also don't like making phone calls, and will invent excuses to myself to avoid doing them if I'm not careful. I'm aware of most of the things I try to avoid, and so keep it in check through conscious effort, but it's something I have to constantly work at.
But ordering food in a strange country without knowing the language, for example? That's fun
I went to Beijing a few years back, and one night our hosts didn't have time to entertain we asked at our hotel for a restaurant recommendation. They tried sending us to a downtown tourist trap, but we refused and asked for something local.
After much arguing (they did not like the idea of sending us walking down the road when we did not speak nor read Mandarin), we got a piece of paper with a carefully written name of a local restaurant that should be easy to find, and walked down the road holding it up to compare it to signs.
Nobody there spoke a word of English, and my Mandarin was limited to about 10 words from a phrase book, but we pointed and gesticulated and got a fantastic meal without any problem.
Like GP, to me if something falls in the "crazy (or not so crazy) adventure" category, it pretty much automatically overcomes my inhibitions. For example, I went to France on an exchange while at school and had no problems walking up to total strangers to ask for help in halting French, while at home I'd have worked hard to avoid having to ask anyone for help.
I wish I knew how to trigger this change at will.