Did you ever, totally go off the JC program for one day and then weigh yourself, the very next day? Only to find that you gained like 6 or 7 lbs over night? I did!
I guess some people have to learn the hard way. Don't go off the program! LOL
Now to get back on track.

Take heart - It takes something like 3500 excess calories to gain a pound, so unless you really consumed 21,000 calories in one day (which I don't think is physically possible), you really didn't gain 6 pounds overnight.
I've never weighed myself afterwards like that, but I have had days where I totally go off program. I think the trick is that when I go off program I tend to eat a lot of salty foods and to not drink enough water ... so try drinking a little more water today than normal and really stick to things today, and you should minimize the long-term damage.

Thanks a million!
Will do!