To regard oneself as an "over-thinker" actually means to spend too much time in the imagination, imagining and playing-out negative scenarios that often don't materialize.
This is also known as ruminating.
Rumination is a common thread among those prone to anxiety, depression and insomnia... conditions which are further intensified from resulting mental fatigue, loss of motivation and feelings of isolation.
No-one has the right to insist you stop thinking so much, after all, not everyone is gifted with a vivid imagination... but if you must spend so much time in your head, at least make it a pleasant place to live.
"...“Oh soul, you worry too much. You have seen your own strength. You have seen your own beauty. You have seen your golden wings. Why do you worry?” - Rumi