I've read that he had prostate cancer in the past. I hate to speculate, but there is always that fear that any cancer could come back in a distant metastasis. If he does have a tumor that might explain the symptoms. That's pretty scary stuff and I would certainly hope that's not the case.
Prostate cancer does not metastasize to the brain. Usually prostate ca spreads to the bones and lymph nodes. These symptoms don't fit with metastatic prostate cancer unless his elctrolytes are whacked do to bone metastases. However, that would be very unusual for someone with good medical care.