A 72-year-old woman is admitted to the hospital with increasing confusion and generalized weakness over the past week. Her medical history includes hypertension, for which she takes hydrochlorothiazide 25mg daily. On examination, she is lethargic but arousable. Her blood pressure is 110/70 mmHg, heart rate is 88 bpm, and respiratory rate is 16 breaths per minute. Neurological examination reveals decreased reflexes. Initial laboratory investigations reveal the following: Sodium 118 mmol/L, Potassium 3.8 mmol/L, Chloride 85 mmol/L, Bicarbonate 24 mmol/L, BUN 15 mg/dL, Creatinine 0.8 mg/dL, Glucose 90 mg/dL. Urine osmolality is 600 mOsm/kg. Serum osmolality is 250 mOsm/kg. Which of the following is the most appropriate initial management strategy?