I have a hard time focusing on the next correct thing to do, and end up playing 3D chess in my head, unnecessarily. I get riled up about a potential conflict/argument, when that conflict may or may not happen. I can literally work through an entire potential episode in my head while in the shower, and run out of hot water.
I've been guilty of this, allowing the negative voice in my head to convince me of all things that can go wrong. Yea, that girl in my head working all the buttons and strings, I fired her.

She was given the job by my FOO originally. Things were just not working out between us because when I flat out told her she was lying to me, she didn't like it and doubled up on the negative possibilities. She had to go, I insisted.
I have a new voice in my head that is more understanding of my fears and tries to put a positive spin on possibilities (opposite action). And sometimes, she reminds me to redirect my thoughts to other things when I shouldn't be over-thinking situations that I either have no control over or things that haven't happened yet in the first place like you say. Things are working out much better, though always a work in progress.