A 64-years-old previously healthy man is admitted to to a hospital because of a closed head injury and ruptured spleen Following a road side accident following an automobile accident. During the first 4 days of hospitalization, following laparotomy and splenectomy, he receives 5% dextrose 0.5% normal saline solution at a rate of 125 mL/h. Recorded daily fluid outputs include 450 to 600 mL of nasogastric drainage and 700 to 1000 mL of urine. The patient is somnolent but easily aroused until the morning of the 5th hospital day, when he noted to be in deep coma. By the after-noon, he begins having seizures. The following laboratory data are obtained: Serum electrolytes (meq L): Na+130: K+1.9; CI 96; HC03 19.Serum osmolality: 260 mOsm/L; Urine electrolytes (meq/L):Na+ 61; K+18. Which of the following statements about diagnosis or treatment of this patient's condition is TRUE?