Personally, I embrace the downtime that I get after finishing a large task. I see it as a way to force myself to take healthy breaks, which are easy to forget when I'm "in the zone."

When I finish a large task, I take a few minutes to think about how I should spend the rest of the day, grab a coffee or snack, use the restroom, check the news, then jump back in.

I even find that, when I forget to take breaks, I'm more easily fatigued and discouraged by what can otherwise feel like an endless amount of work.