I just assumed that my mind is using the "off hours" to process things it couldn't process earlier, at the time they happened, so it shoved it into a mental closet somewhere and when I am not engaged in thinking about much of anything, my brain starts cleaning out those closets. Occasionally, the memory might come before my conscious, making me aware of it, and if my subconscious doesn't know what to do with the memory or gets stuck on it for some reason, it keeps putting it in front of my subconscious to get it dealt with, hence the thing getting stuck in my head. I find that happening after I watch a new movie. For a few days, my brain plays back scenes over and over, I think in an attempt to understand the movie. It can be a week later and I'll suddenly go, "Oh, THAT'S what that line meant!" while I'm doing the dishes. It happens with real memories, too, some of them quite old.
I find that my internal mp3 player turns off when I'm engaged in an activity of interest (unless the thing my mind was working on is particularly troublesome). For me, this is rewatching episodes of Friends or Frasier over and over; I know it's silly, but that's my most intense special interest. Sometimes, it is the only thing that can make my brain go silent for a little while.
Does anyone else notice that engaging in their intense interests make their mental mp3 player go quiet?
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You don't need to hide, my friend, for I am just like you.