Right there with you. I do the exact same stuff in response to uncomfortable memories that I involuntarily obsess over.
I always figured it was just an anxiety attack triggered by the ruminations. Haven’t really found any good coping strategies, though. It is very unpleasant and I wish I could stop it.
Bob would practice each painting 3-4 times before each show. He was crazy fast and achieved that level of speed by rehearsing a few times before filming. Also, his style very often was a bit repetitive, so I’m sure that helped - just sort of mixing and matching familiar elements. Even with rehearsing and the paintings being similar, though, he was crazy fast and consistent.