Over thinking can be detrimental to mental health.
I have BPD and bipolar.
They often refer to overthinking as ruminating, where I will start thinking about something over and over my thoughts keep going over the same thing,without achieving anything.
Often even a nasty comment which the more and more I think about it ends up being a lot worse than it actually is.
Distraction can be good, so I focus on something positive
People say I'm an over-thinker (IRL) however, I would consider myself a deep-thinker... who occasionally speaks outloud, and gets called an over-thinker for it. I think these are two different things, or perhaps more. It's too black and white for me.
IMHO, overthinking may be a symptom per se, though just overthinking does not make you mentally ill per se. I mean overthinking as in obsessing on matters you can't change. I've found a regular meditation practice and mindfulness to be extremely helpful to manage this tendency. Exercise too, I suppose, though I've been a little lazy lately.
Yeah, that's what i figured. I would definitely recommend mindfulness exercises, you can find some on several apps like Calm, Insight Timer and others, it has helped me tremendously with that. Good luck!