Why are humans designed to take breaks?

I find that whenever I have been productive for more than a few hours, I get a desire to withdraw and suspend whatever activity I happen to be doing that day or hour, and I do not know why our body is designed to rest, even when the activity we are dong is not stressful or high intensity in nature or form, is this because the brain wants to process and form new neural connections based on the previous activity and you have to withdraw so that these unconscious processes can begin to align and order themselves in your brain?

Why are humans designed to take breaks?
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