I do the same thing, and I think it helps me a lot sometimes, and not so much others. If you are afraid of something, though, and you try to come up with the various permutations of what might happen, your focus will be on the negative outcomes because those are the ones for which you would want to prepare. I think this is a negative feature of rumination, as it could dig you deeper into a hole. That being said, some of my greatest insights, (if not all), came from ruminating about them. My 2 cents,