Interesting take on the problem of productivity. I've also noticed that when I do design work, design work after design work my design just gets ugly. To solve the problem I do the following:

1. Don't design/code for 2 days.

2. After 3 days, find some article that will get you pumped. Read it.

3. Design/code for 1 hour less than you usually would(for instance I usually code/design for 5-6hours a day, I'd do it for 4-5hours MAX here), take a 10 minute break and then continue. You'll get amazing results. I think this is partly because (like the author of this article said) your brain continues working on the problem.

4. Go to step 1.