The nausea is totally from the die-off of pathogens ... the byproducts that result from the death rattle of all of the various microforms within us (some of them in our stomachs) is a virtual witches brew of toxic waste.
Formaldehyde, Acetaldehyde, Uric Acid ... to name just a few. The body can only handle small quantities of this stuff at a time, and needs a LOT of water to do even that. Any more than it can process, and the body just wants to squirt everything out any available opening.