Whenever I try water fasting (going without food, drinking only water) for a few days, I become extremely ill - I can't breathe.
So many of us are on low-allergy diets, i.e. eating very plain foods, as it is. I think that already makes our sodium intake low. For me the fast made it worse because even my "salty" foods were eliminated.
Then for some reason, my body reacted by having me crave water instead of salt. That's when everything started going downhill fast.