Yeah, a day of not playing is enough to throw me off, and sometimes there are weeks where I don't play.

One thing that helps to get things flowing again is playing extremely slowly with the metronome, e.g. playing reels at quarter=50bpm. Usually the little glitches and brain-fades will manifest even at this tempo, and it's much easier to see what's wrong and fix it.

Warming up physically is equally important, of course -- hot water helps a lot, as does playing very, very slowly.