How bad this is depends heavily on what your diet consists of. It can also be exacerbated by withdrawal from stimulants like caffeine, which tend to coincide with meals.

FWIW when I'm eating a very low carb diet with no stimulants, fasting for a day is a complete noop, pleasant even.

But I also feel nauseous consuming caffeine when fasting. I've come to suspect a major reason people eat breakfast is so their morning caffeine dose doesn't make them sick, though they may not acknowledge it.