Q. A 32-year-old woman with a known history of pheochromocytoma, well controlled with phenoxybenzamine, visits the primary care clinic. She reports a severe headache and palpitations from the morning. Her temperature is 100°F (37.7°C), pulse is 92 beats per minute, blood pressure is 140/94 mmHg and respiratory rate is 14 per minute. She mentions contracting an upper respiratory infection even after getting the flu shot a week earlier. To manage her discomfort, she is currently using over-the-counter remedies, including acetaminophen and a decongestant with pseudoephedrine. What is the most probable cause for her outburst of symptoms?