Oh my gosh I did this to fall asleep nightly when I was younger. I would make scenarios in my head. Usually they were all lovey-dovey about whoever I had a crush on at the time, but I never attributed it to ADHD. I would even focus on tiny details like what we were all wearing or how the rooms/surroundings looked. It really did help me fall asleep though, which makes sense. We force our brain into thinking about only one thing instead of 1000.