One of my friends and I discussed something related to this once. He had helped somebody cheat on a test and had been running all of the worst-case scenarios through is mind for if he got caught. He proposed that our minds subconciously run through the worst possibe outcomes to mentally prepare should they occur.

I think he said that he had read a study on this someplace, but I don't remember if he actually said that or if my memory is just bad. I know that I read our memories can fill in gaps with false information based on the circumstances in which we recall them. There was a series of studies done by Elizabeth Loftus at the University of Washington that confirmed this theory on memory.

Anyways, back to the topic at hand.

What you are talking about isn't exactly the same as what my friend spoke of--- you are talking about it as an exercise to broaden ones horizons opposed to coping with stress. I think it's probably the same mechanism that does these things, though, and you just approach it with a different attitude. Maybe your attitude is a result of letting the subconsious preparation play out longer and also forcing it into the conscious mind.