Kaleigh Levine was running drills in the gym with her lacrosse team at Notre Dame College in South Euclid, Ohio, when everything turned black.

“The coach wanted me to get back in the line, but I couldn’t see,” she remembered.

Her vision returned after a few minutes, but several months and a half-dozen medical specialists later, the 20-year-old goalie was diagnosed with a mysterious condition known as POTS.

First described more than 150 years ago, the syndrome has proliferated since the coronavirus pandemic. Before 2020, 1 million to 3 million people suffered from POTS in the United States, researchers estimate. Precise numbers are difficult to come by because the condition encompasses a spectrum of symptoms, and many people have still never heard of it. Recent studies suggest 2 to 14 percent of people infected with the coronavirus may go on to develop POTS.