I agree, it's a setback. And you can use it to learn more about yourself. Also, I believe that you have every right to sit on the pitty potty. If we can't feel sorry for ourselves then who can, really?
I heard not too long ago that what keeps most people locked in the vicious cycle of disordered eating is shame. The shame we heap on ourselves when we've 'failed'. Made me think about it a bit differently.