One medical worker called it "insane," another said it induces paranoia — the speed with which patients are declining and dying from the novel coronavirus is shocking even veteran doctors and nurses as they scramble to determine how to stop such sudden deterioration.

Patients "look fine, feel fine, then you turn around and they're unresponsive," said Diana Torres, a nurse at Mount Sinai Hospital in New York, the epicenter of the pandemic in the United States, where the virus has infected more than 415,000 people. "I'm paranoid, scared to walk out of their room."

It isn’t just elderly or patients with underlying health conditions who can be fine one minute and at death's door the next. It can happen for the young and healthy, too, health professionals said.