>Thoughts came out of nowhere, I had no control over them; often the constant, unceasing flow of thought was distressing and uncomfortable.

I want to touch on this. "You" never have any control of your thoughts, because "you" isn't really a thing. Psychedelics and meditation teach us this if you pay close attention. The thoughts arise from nowhere and we - the imagined, but illusory - self are mere observers along for the ride that is consciousness.

I can imagine that using a substance such a psilocybin could cause your thought patterns to have both short and long term changes in quality (in terms of substance, not of superior gradation), however. It's also possible that your experience led to your paying greater attention to the thoughts that did arise, and over time the feedback loop of consciousness along with taking better care of yourself led to greater moderation of their genesis.