If you haven't done so, take a proper vacation. Leave your current environment behind completely, don't take a computer with you, and don't allow yourself to so much as think about work.

When I was in your situation, I tried to take pseudo-vacations (i.e. I stayed home for a few days, instead of going to work), but they were never enough. Only by forcing myself to make a drastic lifestyle change, was I able to break out of the fog.