if i have a cheat day like i accidently did the other night had 2 scoops of ice cream, then the next day i do a meat and egg fast and drink gallons of water. i find i get back into ketosis very fast and lose weight.
try not to cheat too often tho, i allow myself a high carb treat maybe once every fortnight. just dont go on a carb binge as it will ruin all your hard work