Don't be sad, it's just a change in their routine. They'll snap out of it. Besides, they may be "punishing" you for deserting them, but I'm pretty sure they're just plain tuckered out. They had a lot of excitement during THEIR vacation, too.
Give it a couple of days ... they'll be OK. It's a shame you don't have a yard: they learned very good behavior during their visit. But, leave the piddle pads out for "urgent needs"
