Try spending ~20 hours in a week playing serious racing sims complete with wheel and real-feeling pedals, then hopping into your car on the weekend to drive cross-state to visit family.

I also got this with programming at least once. I had been spending all night trying to get something with my WPF view models working (and failing). When I finally got into bed, I was having trouble falling asleep because I was just "seeing" endless lines of code scrolling through my head. I very distinctly remember thinking, "What order do I have to call these methods again to successfully enter sleep mode?" Quite a bizarre experience.