Hi,
After I finish a walk several Kilometers long e.g. 6km, either warm summer or cold winter - doesn't matter the temperature, my body undergoes the same sequence like consequent to a sun-stroke, i.e. nausea around the head - especially the forehead corners, loss of appetite, then shitting, then vomiting (if there's anything substantial in the stomach), and then it all comes back to normal. I'm a 40 y.o. man and it started when 39 y.o.
It happens when I either drink enough or not. It doesn't happen when I walk only 3km.