Lack toast & told her aunt - hilarious @vikingbeast.
You’re suffering withdrawals from caffeine, sugar, carbs, … @Vicks1990. It will get better when you’re over the hump (usually about 5 +/- days). It’s called hell week for a reason!
There are several different pre surgery diet plans but just like your post surgical plan it’s best to stick to the one you were given. My surgeon gives different plans to different patients based upon things like starting weight, eating habits, weight loss history, etc.
The pre surgical diet is in place for a number of reasons including to shrink your liver so the surgical field can be visualised more easily, lose weight before the surgery (so you’re healthier) & break some of those food addictions & eating habits. (Better to have the withdrawals now then immediately after your surgery when you’ll have other things to manage.) Between the calories you’re eating & your fat stores you have plenty of energy available for your body function as it needs.
It’s only two weeks - you’ll get through it.