It's highly unlikely that you gained 5lbs of fat in a week....
Seriously, it just didn't happen. Relax your mind, and calm your fears. I will explain why even after a week of being "bad," the scale reading 5lbs heavier isn't something to freak out over.
In order to gain fat, you have to eat more calories than your body burns. 1 pound of fat is equal to roughly 3,500 calories. Let's say for kicks your body burns 1,900 calories per day in its resting state. In order to gain one pound of fat in one day, you would have to eat 1,900 calories + 3,500 extra calories while doing NOTHING. Even moving your body to eat requires energy, and therefore in that situation would have prevented you from gaining a full pound of fat. Make sense? Let's keep going.
If your body burns 1,900 calories a day without exercise, in one week your body would then burn 13,300 calories. In order for you to gain 5lbs in one week you would have to have eaten 13,300 calories + 17,500 extra calories and somehow not burned a single additional calorie. It's not impossible to gain 5lbs of fat in a week. However if you are not someone who binge eats normally you will find it exhausting and even physically painful to eat the amount of food required to gain 5lbs of fat.
As long as you haven't been binge eating for a week straight, those extra 5lbs are mostly water weight, if not completely. Drink plenty of water, and sweat. Those extra pounds will come right off in a couple days. Seriously, don't sweat it. Pun intended. Corny Ri checking out.