This is an interesting phenomenon and again, like heatstroke, something I am unlikely ever to suffer from!
However, my daft little sister Sasha is a likely candidate, as this often occurs in gundog breeds that spend hours playing in rivers and lakes.
Water intoxication in dogs has the fancy name, hyponatermia, and can occur in humans as well as dogs, so it is well worth warning your humans about this. It occurs when you over exercise in warm conditions and then drink a lot of water; this causes the electrolytes (salts) in your tissues to become too dilute.
If this happens, cells in your body start to swell due to the increase in pressure in them; this can affect the central nervous system and the brain and can be fatal. The symptoms to look out for include staggering, vomiting, weakness, bloating, drooling, glazed eyes and seizures – if you feel unwell and have these symptoms after drinking lots, alert your human and demand to go to the vets! If you notice these symptoms in your human, first check that it is water they have been drinking, before suggesting medical attention