Literally just imagining things in your head out of boredom does something similar, and that’s something that’s just gonna happen if you sit idle.

Brains need stimulation to develop and continue to function properly, as creatures with unusually powerful brains, humans benefit from, even need, quite a lot of such mental stimulation. There’s a reason we enjoy and put so much effort into entertaining ourselves, compared to most other animals. Working through imagined scenarios is no more unhealthy for us than exercising our muscles to keep them fit is.