A 28-year-old man comes to the emergency department because of a severe headache, palpitations, excessive sweating, chest pain, visual disturbances, dyspnea. paresthesias, constipation, and a sense of impending doom over the past 2 weeks. These symptoms occur primarily at night. His blood pressure is 130/80 mmHg while supine and 90/60 mmHg while standing; his blood sugar is 240 mg/dL. Which of the following is the most likely diagnosis?