Sorry to hear that Ali. You know, for me, what triggers that kind of thing is when I have been good, ate well, clothes feel looser etc... I congratulate myself, then think I could "afford" to have a few extra snacks at the end of the day... then it's on for young and old!!!
Try not to let it put you off, I'm sure it's just a once off thing. Maybe your mind just needed to take a break from all the "goodness". Get right back into it today, and just forget about yesterday!
If it makes you feel any better, I had a good day yesterday, pretty damn good actually... well, up untill about 9pm, at which time I ate six (count them, six!) tins of tuna, one after the other, mixed with mayonnaise!! That's just wierd in anyone's book. Plus, I take laxatives nearly every day
So... don't stress, it can always be worse