I had something similar happen -- I'd been plateaued for about two months, and I had been watching what I ate really really carefully and exercising, but not losing anything. The one weekend I broke down and ate McDonald's, pizza, and Boston Market, plus a whole bunch of cookies. On Monday, I was down two pounds!! After watching my foods again during the next week I lost two more!
That's not to say that eating a whole bunch of crap was a good idea (I felt SO guilty afterwards) or that eating crap will make you lose weight, but sometimes I think you just need something crazy to get you off a plateau.