I used a program called “attacking anxiety” in my 20’s and one of the techniques they suggested, if I remember correctly, was to catch yourself in these negative thoughts and stop them and try thinking about some more positive thoughts. You would have to get in the habit of being aware of what you are thinking and actively monitoring and changing your thought processes to get this to work. It’s work to do this, I know.
I experience this almost constantly, I’ve mentioned it before on this website. My mind is almost constantly in analytical thought mode. When I learn something new it causes me to rethink things. I don’t know how to stop it. They are not racing thoughts, or anxious thoughts or delusional thoughts. They are rational thoughts, but they happen constantly. Occasionally my mind is calm and I just take time to enjoy that when it happens.
I have struggled with this my entire life. Natural worrier. Ever since I went on the max dose of Cymbalta I stopped with the constant worrying and overthinking. I still get anxious about certain things from time to time but it’s not the constant chewing.
I have lots of ways to deal with this but it remains a difficult problem for me. These work sometimes:
I disregard my thoughts and shift my focus to a body scan meditation, i.e. what physical sensations can I notice. I can also focus on senses, like sight, sound, touch, smell, and focus on my breathing.
I force my thoughts to slow down. I know that I cannot stop thinking entirely, buuuuuuuuuuuuuuut iiiiiiiiiiiiiiii caaaaaaaaaaan maaaaaaaaake myyyyyyyyyyyyy wooooooooorrrrrdds reeeeeeeeaaaaallly loooooooooong. Usually my brain gives up bothering me after 5 minutes of being trolled this way.
I have a mantra “everything important is known”. It reminds me that I survived this long without needing to know whatever is bothering me. And that if whatever is bothering me is truly important, then I will remember it tomorrow. So I don’t need to obsess about it. If tomorrow comes and I forget it, then it wasn’t important. This sometimes brings me relief from worries and obsessions.
If I am really struggling then I’ll ask my other personalities / voices to help me. In other words, I wilfully dissociate / depersonalise. This isn’t a recommended solution, because it comes with an anxiety hangover.
Self-punishment can work. There is a punishment zone in the brain, that shuts down dopamine, and this reduces neurotransmitters, which inhibits overthinking. The tricky bit is to do this in a safe way, and not self-harm. I save this one for real emergencies. I use a tiny pin, and just prick my leg very lightly, not penetrating the skin. Beware though because it is addictive.
Maybe you could find someone who can give you guided meditation or mindfulness. They are techniques. Usually work or doing something you don’t like doing brings you back in the here and now. Making bread was the ideal job for me as I overthink too.
Do some arts like drawing or music.
Do some writing/journaling where you go over your issues and just get it out onto a page.
Sometimes just sharing with other people can help if you have people you trust who are supportive.