This can be from leaky gut (intestinal permeability)... and Larazotide Acetate might fix this for you. I just started LA, so I'll let you know if my nausea goes away w/ this treatment.
Studies have shown that ME/CFS patients post-exercise had increased bacterial translocation... where the exercise increased the amount of bacterial toxins that were escaping from the gastrointestinal tract.
This happens when the tight junctions in the intestinal epithelium are no longer "tight"... like, basically holes developing in the barrier here, allowing toxins from the gut to escape into the bloodstream.
The leaky gut idea is strongly linked to ME/CFS. In my opinion, if exertion causes strong nausea, you have very high levels of leaky guy or intestinal permeability. (I also believe that certain EV strains are more likely to cause this... like Echovirus 11, which I have, is well known to massively disrupt the intestinal barrier. I think this is why we don't ALL have this type of nausea)
Larazotide Acetate will seal up and repair the tight junctions. At the lower dosages, it's been shown to greatly improve nausea symptoms in those w/ Celiac Disease.
This happens from Enterovirus that lives in the intestinal epithelium. It eventually causes leaky gut here. Enterovirus is a top suspect of both ME/CFS and Celiac Disease. Other viruses involved in Celiac, like Rotavirus for instance... this also will persistently infect the intestinal epithelium and lead to leaky gut.
LA isn't a permanent solution... but it could fix symptoms for a while