<prompt> A 32-year-old man is feeling unwell and brought to the hospital. His serum sodium is 125 mEqL. On examination, his blood pressure is 11070 mmHg, pulse 110min supine, and sitting up causes him to feel lightheaded with a drop in his blood pressure. His urine sodium is 5 mEqL and urine osmolality is 800 mOsmkg.For the above patient with hyponatremia, select the most likely diagnosis.congestive heart failure CHFextrarenal sodium and fluid lossesSIADHpolydipsia  <response>: The combination of ECF volume contraction and low urinary sodium 10 mmolL suggests extrarenal sodium loss. Common causes are vomiting, diarrhea, or excessive sweating. 