Two years ago, Ratona Harr, 46, was teaching the same Saturday morning fitness class she always taught. But this time, the class didn’t go according to plan.

About 20 minutes into the cardio-focused session, “I felt like there was an explosion in my chest,” Harr, who owns Full Body Fitness & Yoga in northern Kentucky and also teaches at CycleBar, tells TODAY.com. “It was like somebody punched me in the chest; it was just immediate.”

Harr tried to push through, but when she went to pick up a weight, she realized her left arm had gone numb. She began to lose feeling in other parts of her body and noticed that sweat was “just pouring off” her, she says.

Harr tried to walk down the hall to the bathroom. “I’m desperately trying to breathe and figure out what’s wrong with me,” she recalls, but she couldn’t find her balance so she “was just kind of flopping around in the hallway.”

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At that point, a few of Harr’s clients who also happened to be nurses called 911.

“Class started at 8:30 a.m., they called 911 at 8:56, and by 9:33 I’m getting two stents in my heart because I have 100% blockage in the main artery in my heart,” Harr recalls. (A stent is a small tube used to hold open an artery or another passage in the body.)

Read more: Today