AVP and inappropriate ADH syndrome: Despite initial suspicion of the syndrome of inappropriate antidiuretic hormone secretion (SIADH), caused by elevated antidiuretic hormone (ADH), the patient's normal osmolality and sodium excretion suggested other contributing factors, such as poor oral intake (per os, PO), volume depletion, and pseudo-acute kidney injury (pseudo-AKI) leading to hypovolemic hyponatremia.