When I've had that, I've assumed that my body is trying to tell me something other than chippy chips are the best and added in some extra protein/fat in the next couple of meals - after all, if you suffer for days and then give in and go completely overboard, it's going to stall your progress more - with an extra side helping of guilt and self loathing.
Is there something in particular, a flavour, for example, that you're craving? Could you be dehydrated and need both more water and a little bit more salt? Is it that you are actually doing significantly more than 2000 kcals of merely existing a day? What is your body telling you that you need?
I got collared by somebody this morning to tell me exactly that. It's nice to hear it.
Oh, and I got much praise from the physio, so much so, she's keeping me on the books to see if anything else crops up over the next couple of months of exercise, so I'll see her again in July.