Oh no.. none of us EVER have bad days where we eat mindlessly..
And if you believe that, I have a great deal for you on a bridge in a major metropolis...
In a more serious vein. Everyone has these lapses. Sometimes they're emotional eating, sometimes stress, sometimes other things. I think that success comes not from never having lapses, but from learning over time how to deal with them and minimize the damage.
Something that helps me sometimes is to try to figure out what I am really craving and have some of that. If I try to eat from my normal healthy choices, often I eat more than I would of the craved food, because the healthy options aren't really satisfying me, if that makes sense.
You're doing a wonderful job. You've got six weeks of healthy eating under your belt, and now that you've had a lapse you're looking at it, figuring out the cause, getting advice to deal with it. You go girl!