Any reason why? Any way I could fix it?
Likely it was from lack of electrolytes, but even things like how well you slept or what you ate the day or two before starting can have this effect. You shouldn’t feel nauseous while fasting, so it’s good that you stopped, but it’s not an uncommon occurrence. Regroup and try again another day.
Sometimes my hunger and nausea cues get confused, so I feel nausea but my body is telling me it expects food either out of habit or a dip in blood sugar.
I typically don’t need to add any electrolytes if I’m fasting for 24 hours, but it’s worth seeing if a pinch of salt helps you feel better. If that sounds unappealing you can do a dirty fast and get the sodium by drinking a cup of broth.
It may be worth easing yourself into 24 hours by trying 16 hours, then 18, etc.
Good luck!