A 62-year-old woman with type 2 diabetes mellitus on metformin and glibenclamide presents with a 5-day history of progressive confusion, weakness, and polyuria. Her family reports she has had recurrent vomiting and has not been eating well. On examination, she is alert but disoriented, respiratory rate 16/min (not laboured), blood pressure 98/60 mmHg, heart rate 118/min, and skin turgor is poor. Capillary refill time is 3 seconds. Laboratory investigations show: blood glucose 1020 mg/dL, arterial pH 7.32, HCO₃⁻ 18 mEq/L, anion gap 12, serum sodium 122 mEq/L, serum osmolality 385 mOsm/kg, serum potassium 5.8 mEq/L, and serum creatinine 2.2 mg/dL. Urine dipstick shows no ketones and no protein. What is the most likely diagnosis and the key distinguishing feature from DKA?