I have this exact problem even without the travel... A couple of days at home without continuous jobs / tasks needing to get done. Great, I can finally get onto doing some work for project X!

Except it never happens. Seems my motivation / drive is so depleted that the best way to use the days off is to actually rest. Then I feel great (although generally a little miffed that I didn't get anything done on project X) and for the next several weeks I seem to have more focus and be able to get my everyday things done more effectively.

Sometimes the best way to utilise a break is exactly that - have a (complete) break and just rest the mind - I find some physical exercise (surfing) helpful with that too.