'Strokes and heart attacks don't take a vacation.' So why have emergency department visits sharply declined?

Across the country and the city of Boston, hospitals are reporting precipitous declines in emergency department visits, even as coronavirus cases climb. The phenomenon is as perplexing as it is alarming — at least as it concerns medical emergencies like appendicitis, heart attacks, strokes and even acute psychiatric problems, for which there is no intuitive way to explain the staggering drops.