I feel you about getting antsy when you’re not productive, or feeling a project won’t get worked on without active effort on your part, but one thing that helps me slow down is two pieces of knowledge.
One, that a ton of the processing your brain does is unconscious. You ever go for a walk to “clear your head” and suddenly a solution popped into your brain? Your mind never stopped working on the issue, it just got put outside your conscious awareness.
Two, that operating at lower efficiency for longer is exactly what tanks you and brings you down to zero efficiency (and also kills your ability to process unconsciously). You ever heard “fast is slow and slow is fast”?
Don’t think of it as being unproductive: do you think a car refueling is being unproductive? Or is that and an oil change part of routine maintenance that keeps you from needing to push it down the road to a station every so often?