In a COVID-19 "second-week crash," patients believe they're recovering but then feel much worse.

Business Insider reports people who've experienced them firsthand say second-week crash symptoms include shortness of breath and body aches.

Health experts don't know why only a subset of the population has this second-week crash.

It often results in a high fever, shortness of breath, and extreme fatigue.

There was a pressure, too — as if someone were squeezing my lungs like an accordion.

My breathing felt heavy.

Aria Bendix Presumed COVID-19 positive Dr. Christopher Ohl is an infectious disease expert in North Carolina.

He says he's noticed a rapid decline in health for many patients.

They say, 'Hey, you know, I think I'm getting over this,' and then within 20 to 24 hours, they've got fevers, severe fatigue, worsening cough and shortness of breath.

Then they get hospitalized.

Dr. Christopher Ohl