A 60-year-old male with a 5-year history of hypertension (HTN) presents with 1 week of cough and fever. Today, he was found unconscious by family and brought to the emergency department. Examination: altered mental status, epileptiform convulsions, pulmonary rales/crackles, heart rate 110/min, BP 130/60 mmHg, questionable left Babinski sign, WBC 13–13.5 × 10⁹/L, urine glucose (++++), ketones (-). The most likely cause of coma in this case is: