A 25-year-old male developed dry cough and chest tightness 2 days ago without obvious cause, followed by wheezing, which was unresponsive to intravenous aminophylline. Over the past 3 years, he has had episodic cough and shortness of breath in autumn. Examination reveals orthopnea, cyanosis, decreased breath sounds with scattered wheezes bilaterally, normal cardiac size, no murmurs, pulse rate of 120/min, and pulsus paradoxus. The most likely diagnosis is: