It wasn't a steady state. It was more like losing myself completely in a piece for hours, something close to what people call 'flow', followed by the return to a kind of restlessness that never fully went away. It wansn't just the background noise I tolarated, it's pulled me back into the work the next time.
So I am not sure the essay's framing, chase meaning intead of happiness and happiness follows, is quite right, at least not for creative work. It might be closer to a cycle: immersion, then unease, then immersion again. This restlessness isn't incidental to the meaning, it's part of what generates it and I wanted to keep it. Otherwise I was afraid, I will loose the ability and motivation for creation at all.
Curious if others who do creative or deeply absorbing work recognize this pattern, or maybe are lucky ones who are able feel satisfaction of their progress and growth.