Could be obsessive thinking, ruminating. Fortunately there is literature on the subject. Unfortunately, obsessive type stuff is difficult to deal with.
You'll get through it.
I try to set aside at least a half-hour a day for meditation, myself, lately. It has been helpful at times, I think. Other times, it hasn't seemed so helpful.
Isolating, living alone, shutting the outside world out: these sorts of things often make for fertile ground for neurotic type stuff to fester, unfortunately. It can also be good, though, too, for self-reflection, and healing.
Researching, hitting the books, having a routine, having understanding and supportive people... These things can help, mileage may vary, though. Counseling can be hit or miss, if you can afford it, even...
I have found nervous illness type stuff, to be like the Chinese finger trap. When nervous tension arises, you become ensnared in the trap. You try to pull away from it, and it tightens even more. But, if you go towards it, lean into it, it loosens, and with the proper knowledge, you use your other fingers to remove the trap from your index fingers, and you are free!
Tough stuff though
Life is unrelenting some times...
If it's just over-thinking and a mind that won't stop, still, again, meditation can be helpful, or mindfullness. The therapy circuit is big on mindfullness and adult coloring and stuff. I used to keep a puzzle on hand, to 'untangle,' my mind, so to speak. The nice thing about completing a pretty puzzle, is you can glue it on the back, and hang it on the wall, frame it, display it. You get a little fruit for your labor. Or you could pick or do most any kind of craft, maybe even try to sell the stuff you complete, I've had a hand at that too, with very minimal success mind you.
Masterly inactivity, they call it. Some times, it's the busy-ness of life, that destroys us, and some times, a structured routine, of 'staying busy,' is what saves us in the end...
Idle hands, and such...
As for me, bleh... I'm tired of trying so hard; but, gotta keep flowin'... **** all that busy nonsense. It's destroying the world. But I think one can still manage to, 'stay busy,' with out getting involved in, 'busy-work.'
Good luck Miss LadyGray
(That's the one nice thing about meditation though (or quiet contemplation, prayer, etc.., all very similar stuff). I think if you can figure out how to do it properly, you cleverly come up with a way of doing something, by doing nothing.)