The mind with its thoughts can make us feel all kinds of uncomfortable things. What we try to learn when practicing mindfulness is that those thoughts do not represent reality. They are not truths--they are delusions, so to speak.
That's why we should practice letting these thoughts go, understanding that they hold no truth. May these thoughts be our fears, our judgments or our regrets, it doesn't matter.
That is all clear if we understand the basics of mindfulness. The hard part is that these thoughts bring feelings with them. Feelings that are uncomfortable and are not so easy to shake. Feelings that we want to run away from.
Thoughts have brought feeling with them, and we should accept their presence. It is important to understand the following:
The body doesn't see the difference between an imaginary threat and a real one.
Which means that our body will react to our thoughts as if what we're thinking about was actually happening. The uncomfortable feeling is not there because the threat is real. It's there because our body doesn't know the difference. That's why we have to step out of thought and realize that our body is only reacting to an imaginary threat.
This may not be the easiest process, since the uncomfortable feeling and the untrue thought feed on each other. The feeling validates the thought and vice versa.
There is one thing we can do when faced with a situation like this. And that is to react with a peaceful mind.
Because think about this: Is there any situation where a peaceful mind wouldn't be useful? A mind at peace only makes every situation clearer, so we can react to any situation as best as we can. A peaceful mind is always a good thing.
A mind in chaos, however, is never a good thing. It never aids us, it never helps any situation. So overthinking and worry is never beneficial. It does no good to anything, and it only makes us feel a lot worse than we should be feeling.
A situation is never as bad in real life as it can be in the mind.
So what you can do to step out of the thought-cycle is to slowly allow your mind to calm down. To make it a peaceful place. When a worrying thought comes into your mind, recognize it as untrue, recognize it as just a thought, and create peace inside your mind.
That is the only thing you should do. It doesn't matter what your body is feeling because of the thoughts you have already entertained, what matters is that you restore the peace inside your mind. Accept that the body is uncomfortable right now and concentrate only on the mind. When you create peace in the mind, your body will soon follow.
The body only reacts to its center of intelligence, which is the mind. If the body is in distress because of the thoughts in the mind, the only way to remedy that is to calm the mind, to work with the thoughts inside of it.
So, to sum it up, always aim to have a peaceful mind. Whatever happens, a mind at peace will always be your ally. And all the worrying thoughts your mind sometimes wants to think? The only thing those do is make you feel bad. They were never true anyway.
A guided meditation on the topic can be listened to here.
"If you realized how powerful your thoughts are, you would never think a negative thought." - Peace Pilgrim