not being able to drink is related to salt imbalance, specifically drinking too much water without enough electrolytes in it. I figured that out beyond any doubt on that dnf'd 600k last year, very unpleasant.
I sorta knew that and thought I had it covered. I think that I might have had too much salt on Saturday's ride, can't be sure. But also, I was sick for 2 weeks, so that didn't help. Also sick for the start of last year's dnf. Can't buy a break.