OK, Renee, let's say you've been a very good low-carber for a month and you suddenly spend a whole day eating LOTS of carbs.
First of all, your body will have high blood sugar from digesting all those carbs. Insulin will shove all the extra sugar into your fat cells so it can be used later.
So, do you start over? Well, you have to go back to eating low-carb long enough to clear your body of all that extra insulin floating around and long enough for your body to run out of easy fuel.
Your body is smart. It stores large amounts of excess sugar in the fat cells for long term use. However, there are times when the body needs quick fuel. It stores some fuel in your muscles as glycogen. Now, you have to use all this glycogen up before your body will open those fat cells and use the fat as fuel. That's why it often takes a couple days to start burning fat again after you've had a carb binge.
If you keep eating low-carb after your binge, you do recover in a few days, depending on how much you exercise, how much water you drink, etc.
If you have more questions, or if I haven't explained it clearly enough, please feel free to post! I love to discuss the technical side of why low-carb eating works and I really do try to make it easy to understand.