I think everyone rehearses/imagines conversations/interactions to greater or lesser degrees. So, in that sense, it's totally normal. But when it's having negative impact, then it's a problem, and like others have mentioned... "mindfulness", being in the present, all that stuff is a good approach to deal with it. Then there are the tapes in our heads. Mine are very noisy too. And negative. A lot of them have been playing so long, they're default.

Imagining all sorts of situations? Oh yeah. If there's a possibility -- no matter how unlikely -- I've probably run it around and around along with 300 others. Worst possible? Of course! Special consideration given there. Drives BF up a wall. "Over-thinking", he says. Haha, he's said, "nobody thinks like that!" to which of course I reply, "well somebody must, because I do!". Unlike some of what you describe, mine don't make me project onto situations so much as somehow feel "prepared". It's probably not as useful as I'd like to think, though. I've had far better luck recognizing "tapes" to challenge them. The 10,000 possible scenarios whirling 'round and 'round is out of control. (I have other issues besides BP, which probably don't help.)

Anyway! Being aware of them is a big deal, so good for you, johnf! We have to recognize them before we can work on them, you know?