- replaying some sort of argument/confrontation or other high-stakes conversation from earlier in the day (simulating ways the conversation could have gone better--the best zingers are the ones you come up with in bed at night).
- preparing for an important presentation or meeting the next day (informal rehearsal).
- out hiking alone (especially longer solo backpacking trips). Without fresh content bombarding my brain, I tend to dwell on the same ideas/conversations.
- reading a particularly engrossing book, and get into a character from their point of view.
- studying something new, then I imagine myself tutoring someone else on the subject (my go-to learning technique).
Now if you find yourself having conversations that you were convinced are real at the time, but it later dawns on you that it never actually happened, then that might be something to talk (for real) to someone about.