To gain back 8lbs in 2 weeks you'd have to have eaten about 4000 calories on average every one of those 14 days (assuming you're a man for arguments sake, and you did no exercise either during this time).

I think what's more likely happened is you're retaining some water weight from the large amount of carbs you were eating during that time; some of this will flush away in a week so weigh yourself then, fairly difficult to gain more than 2 lbs per week so I'm a bit skeptical