A 12-year-old female with a past medical history of anxiety presents for emergency laparoscopic appendectomy. During preoperative evaluation, the physical exam is notable for a fine tremor but is otherwise unremarkable. Anesthesia is induced with propofol, fentanyl, and rocuronium and maintained with sevoflurane. Twenty-five minutes after incision, the patient develops tachycardia, truncal rigidity, and a rapidly increasing end-tidal CO2 despite increased minute ventilation. Increased temperature and metabolic acidosis are identified subsequently. Which of the following is the MOST likely diagnosis?