A new arrival: evidence about differential diagnosis

You are a primary care physician seeing a 53-year-old man who was examined 2 days ago in an emergency department for an episode of syncope. He had been waiting in a long line when he felt lightheaded and nauseated; then he lost consciousness, with no witnessed seizure activity. He has been healthy, with no known cardiac or neurologic disease. In the emergency department, his vital signs and findings on cardiac and neurologic examinations had been normal, as were his blood count, blood glucose level, and 12-lead electrocardiogram. He was given no diagnosis, and he is now worried about what caused ...