There was a period in my life when a mantra(?) of sorts was stuck in my head. Just a short phrase or word (I think actually for a long stretch the number "256" was stuck in my head). For reasons unknown to me I would repeat the phrase in my mind or under my breath — seemingly as a way to either keep focus on some current thought or to derail the current thought. I don't remember which.

I think I was under a lot of stress then — I have worked on a team or two where the project (and management) were stressful. So likely that is it.

(Also a tell: I began to notice my handwriting when I signed checks was deteriorating to something scrawly, uncontrolled — when I switched teams and made other changes in my life to reduce stress I found my signature return to the more graceful strokes I was used to.)

Musically, there is (still) often a song stuck in my head. But I put music on in the background nearly every day, seems to keep the song in my head moving along to something new....

I never really made a connection with music getting stuck in my head, but I often get short phrases or words stuck in my head on constant repeat for days at a time too.

The stress relationship may have something to do with it though. The times where it happened the most are pretty strongly correlated with high periods of stress in my life as well.

It often happens for words that I realized I was pronouncing wrong from only having read them and never having heard them. For example, sepulcher and dais come to mind as words that I repeated internally with no control for days on end and they're both words that I was mispronouncing until I heard them while reading and listening to an audiobook at the same time.

Interesting little quirk of the mind I suppose.