What would cause dehydration to the point of nausea?

I mean I survived Rio Do Janeiro Brazil, I survived the summer heat at Iguazu falls by both Argentina and Brazil, I survived a hot 35 degree day with full summer sunshine and then I get dehydrated when I spent the entire day in my hotel room drinking juice and coffee and water and eating low calorie foods. I also slept beautifully last night and the night before.

What would cause dehydration to the point of nausea?
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