I was just reading earlier this this week that polydipsia (excessive water consumption) is not uncommon is patients with schizophrenia. Of course, I have no idea what happened here, but that might be one way the facts could fit together.
Polydipsia, along with polyuria (having to pee a lot) is also a symptom of diabetes. It's possible that the captain had a diabetic episode. Very low blood sugar can cause symptoms that look a lot like schizophrenia. So rather than a mental case, maybe this is just an illness.