Would one big cheat day to myself mess up the weight loss streak I have going on? Does it all restart?
No, it will not. Think of it in numbers. For example, you were at a 500 calorie deficit everyday from Monday to Saturday. That’s a 3,000 calorie deficit. By Sunday, you have your cheat day and you ate at a 1,000 calorie surplus. That still means that for the week, you were at a 2,000 calorie deficit.
It will set back your weight loss a little bit, but it wouldn’t waste your fasting streak.