I've had sleep problems for years. I can't stop thinking. A lot of the times my legs need to be moving a bit too, so I have trouble sitting still while sleeping. I've recently developed teeth clenching, for some reason (not good at all, so now I have to focus on not doing it).
One thing that can be quite common for me is games will play out in my head. Usually not completely structured, but the basics of that game will be done. After I started playing DDR, I'd have arrows scrolling through my head while trying to sleep. One game, a capture the flag style game, I'd have the basics of that play out as well.
I had gone through a phase at one point of having these kinds of awkward conversations in my head. I'd be thinking about something, and then suddenly I'd involuntarily ask myself an important question about the subject of thought, and before I could even consider an answer, I'd forget what the question was, and sometimes forget the entire subject I was thinking about.
One of my newest things while trying to get to sleep now is I'll hear in a very very clear voice, as if it was in the room, my mother saying my name, and then I'll lose all progress I'd have in getting to sleep.
Trying to get to sleep sucks, and it can take me a long time sometimes.