We have all been there. Thoughts go on and on in our minds, hopping from one to another, often via seaways that make no sense whatsoever.
This overthinking and rumination is indeed a significant source of stress and suffering.
I am here to let you know that there is indeed a way out. What is the way out? Going in, deeper.
We tend to think of our thoughts as immaterial, ghostly "things." But how do you know they are there? Because you can hear them.
This voice in your head reads out loud all of these thoughts.
Step 1: Listen to the voice in your head objectively.
Observing these thoughts and listening to them as if you were listening to someone else will be the first step. Then, view all of them objectively.
Notice what your interlocutor is saying. Does it make sense? Are you listening to a crazy person? Is that person trying to fool you or to trick you? Is that voice on your side or against you? All of these answers don't matter. We listen and notice what is being said.
We release our attachment to the substance of that monologue.
By letting go of the emotions we tend to have towards these thoughts, we will start gaining control over them.
Step 2: Noticing that you are not that voice, but the person listening to it.
Step 2 is noticing that because you can listen to that voice in your head, there are now two "yous." The first you is the one talking, and the second you is the one listening. The fact that you can start telling the difference between the two characters is an essential step towards enlightenment. You begin to realize that you are not your thoughts, and so you must be something else, something more. You are not the thoughts in your head, so you are even less the thoughts of you in other people's heads. That new perspective is crucial in understanding who you are - and opinions others have of you are also these thoughts that are not you. Enjoy the freedom granted to you by that realization.
Step 3: Practice via meditation, catching yourself lost in thought.
Step 3 is to practice catching yourself being associated with your thoughts. When you start thinking, you will go back before step one a lot of the time. That means that you will be confused by what the voice in your head says and whether you are that person or the person listening to it. You must catch yourself and go back to listening to these thoughts objectively. This will become easier with practice, and there are some exercises that you can do that will help you. Meditation is one of them. Meditation is a great exercise to gain that skill of catching yourself overthinking and going back to who you are - the observer, the listener. You will start realizing that most of what the voice in your head is telling you is insignificant meaningless - a waste of time and a massive waste of emotional energy. There are no shortcuts. You will have to practice, and this will all become more natural through time. There are hundreds of ways to meditate. If you are interested in how I do it and teach it, I post free guided meditations on youtube and my podcast. If you would like to go further and practice with me daily, you can look at my daily meditation page.