Recently, I overheard a nephrologist, a resident, and a med student discussing a psych/med patient with hyponatremia from psychogenic polydipsia. The nephrologist was arguing that a patient couldn't maintain that significant degree of hyponatremia just from drinking lots of water.
Nephrologist: "Hey, we have a third year med student... we can experiment on her."
Med student: "Huh?"
Nephrologist: "So she would have to drink about a liter and a half of water every single hour, right? Actually, she's small, so maybe only a liter. She'd have to drink a liter an hour every hour, 24/7."
Med student: "I think I'd get tired..."
Nephrologist: "What do you think? Could she keep it up?"
Resident: "I don't know. Is she a psych patient?"
Nephrologist: "Well, she seems like a pretty nice girl. Also I don't think they let psych patients into medical school. So is it possible?"
Resident: "I think it's possible."
Nephrologist: "She'd have to keep drinking while she was peeing."
Resident: "You mean you don't do that?"
Nephrologist: "Yes, but I thought I was the exception."