"constant thinking" is a correct and usable phrase in written English.
It is commonly used to describe a state of mind or a process of mental effort, usually in the context of problem solving or decision-making. For example, "He was trying to come up with an answer, so he put his mind to constant thinking."
"Even in the times when Margaret's not speaking, there's constant thinking going on, there's a huge rich inner life that's happening.
Right now I don't have the same stresses or pressures that constant thinking about the next day's work.
Qualitative job overload was measured with a three-item scale which consisted of the items 'requires concentration', 'complex job which requires a high level of knowledge and skills' and 'requires constant thinking about the job during work hours', with the same response scale.
It's constant thinking and talking and wondering whether to push something or not push it.
This is the secret charm of the program -- it necessitates constant thinking, planning and decision making in a way that makes just watching football on television seem boring by comparison.
I wore out from the constant thinking, abstracting, analyzing, and re-analyzing the stream of nonsense.
It's a constant worry thinking about finding extra money".
Through your constant moving, thinking and rethinking, you fail to see the deer snacking on the forest floor.
The three of us have managed to create an intense environment of constant challenge, thinking, creating, meditating, and empathizing.
Like the author of "The Nasty Four-Letter Word That Keeps You From Writing," (which I highly recommend to any writer), I often live in constant fear, thinking that my career, my life, any success I may have is just a fluke.
This ingredient is a near-constant when thinking about refreshing dishes; all that water content helps us to hydrate, and, when it's straight from the fridge, to keep the temperature down.
