A 40-year-old woman experienced psychological stress 3 months ago and has had poor sleep since. She suffers from unbearable thirst, requiring large amounts of water intake even at night (4-5 thermos flasks daily), with a preference for cold water. Urine output has significantly increased, averaging once per hour, including over 5 nocturnal voids, totaling 9L/day. She has been irritable, with weight loss, and developed headaches in the past 2 weeks. The most appropriate treatment for this patient is: