You may feel trapped. Trapped with thoughts, you are clueless about. It is like someone is just forcing you to think about everything that you do not want to think. You end up thinking about things that possibly have no existence in reality or the least chances of happening in reality. The more you try to end the chain, the more you feel trapped. Isn't it? Overthinking is like a vicious circle and, you might feel, that there's no way out.
If you can relate to all the above things, then the first thing, you need to understand is that your thoughts/brain is controlling you. Your brain has become your master, whereas it should be the opposite.
The only person that can save you from overthinking is YOU. If you want to stop Overthinking then, you need to take charge of your thoughts. There are many external sources like books, motivational speakers, and more, but what is gonna help you out is YOU. Find what triggers your mind, and start putting efforts on that part. There are innumerable techniques available on Google, implement them in your life, and find that one best technique that helps you in minimizing or stopping overthinking.
How Did I Stop Overthinking?
I implemented numerous techniques and finally sorted out a few, which helps me in restricting my thoughts. It's not easy, but it's YOU who can stop these thoughts.
1. Whenever I think that I am overthinking, I always speak to myself - THESE ARE JUST THOUGHTS. THEY WILL COME AND GO. I AM NOT MY THOUGHTS. This makes me realize that I'm on one side of the line, and my thoughts on another. Just 'thinking' is not going to help me, but my actions are going to help me.
2. Self Assessment: It means to identify your thoughts, write them down, and then understand that whether it's worth-stressing over or not.
For example:
"I think, I'm going to fail in tomorrow's test." - I don't know the future. So, let me just work hard and leave the rest.
"I want to buy a Mercedes, but I don't have enough balance." - Right now, my reality is not supporting me to buy Mercedes. But I will work hard, and save enough to buy one in the near future. It is a waste to stress over this thought right now.
These two techniques have been proven beneficial to me, but that doesn't mean it will be beneficial to you as well. You need to try them out, and then only you will know. Also, it is not at all a one-day process. You need to put effort and work continuously.
Your reality is not as bad as your thoughts make it.