What a great thread. As you've said, everyone has these moments, however irrational they may be. When I find myself freaking out, I actually go back to two things one of my first instructors taught me (at Alpine Meadows, he was a fellow Aussie from my home mountain which was funny) when I was an 18 year old real beginner. It was to pretend you are holding a drinks tray as you ski thru and you don't want to spill them, and the other is the steeper the pitch, the more you lean forward... I think it's just the fact that I can focus on something that I know has helped my skiing in the past that does the trick... focussing the mind I guess!
The other thought I had is that the more you ski, the more used to different terrains you become. Even tho I am not an expert skiier, all those years skiing ice, crud, and crappy conditions in Aust and other places means that when I come across them now, I can go, yes this is crap but I know how to get thru this. And side-slipping is absolutely so important, I've been teaching my kids how to do this too.