Getting back in the saddle is really difficult for me because when I check out of something I really divorce myself; vacations for me are for family and relaxing (and sending @ryan inappropriate text messages) and I struggle getting centered when it’s “once more unto the breach.” I try to just concentrate on one small thing (typically not vital or critical path, so it’s ok if I take longer than really necessary) and get that done, and that starts the pistons firing on all cylinders again.
On the other hand: if I see myself losing motivation or center when I’m working on something…I walk away. I try to concentrate on something else entirely to distract myself and then I let gravity pull me back into what I was doing before I lost my way. It’s like when you’re doing a home improvement project and you get stuck, best advice is to take 10 and walk away, you’ll find you come back and solve the problem by taking the minute to distract yourself.
Works for me, but YMMV!