Short answer

There are 2 ways of thinking, which are the relax parasympathetic and sympathetic way of thinking. Parasympathetic is the preferred way of thinking nowadays.

Introduction

Thinking requires quite a substantial amount of energy, and lots of people nowadays are stress due to overthinking. This stress coming from overthinking causes our body to be tense most of the time and ultimately leads to a lot of diseases like insomnia.

Sympathetic vs parasympathetic thinking

Parasympathetic thinking is to think in a relax way and sympathetic thinking is to think in a tense and stress way. Sympathetic thinking is required when you are in a danger situation and fast reactions are needed to survive. This is good during our human evolution in order for us to survive from the attack of other animals and situations, but this stresses our body. Constant sympathetic thinking will lead to accumulated stress and problems in our body. Our body haven't had enough time to adapt to our new environment, where our daily jobs require constant thinking. We need to be mindful and train to switch our thinking into parasympathetic mode.

Identify the mode of thinking you are using

One of the ways to know which mode you are using when you think is to observe your breath and your body, especially your diaphragm area. This observation requires attention to the subtle details of your breathing and your body, which meditation will help to train and enhance the skill for the observation of your body.

When using sympathetic mode of thinking, you are fully absorbed into your thinking and the present moment environment becomes oblivious to you. You will know this when you are thinking and not aware of whatever happens around you for a small period of time, like when someone is talking to you and you are focusing fully on your thinking. You will also tend to have a cloudier mind compared to parasympathetic thinking, which produces less creativity and less preferable results.

Conclusion

Both parasympathetic and sympathetic thinking are useful but if we are constantly under sympathetic thinking, we will have constant stress on our body. We need to train to switch to using parasympathetic way of thinking in this contemporary world which requires constant thinking to solve our daily problems. Think in a relax way.