Crystal Thornton had a seizure during the concert’s opening act, according to information Vanderbilt Medical Center provided to CNN.

“She stopped breathing, her eyes rolled back in her head, and her body started twitching,” friend Christina Tugman told CNN. “I was asking if she was OK, and she wasn’t responding.”

Tugman ran to the lobby. EMT supervisor Jerry Jones reached Thornton about a minute after being alerted to the problem where he found Thornton unconscious with no heartbeat. It took Jones and other paramedics more than five minutes to revive Thornton using a portable automated external defibrillator, according to CNN.

Vanderbilt spokesman Craig Boerner told the Tennessean medical personnel define death as being “without a heartbeat for over 5 minutes.”

Thornton is apparently doing well at press time but she went through extensive treatment. First, she was airlifted to Vanderbilt’s emergency department where doctors used therapeutic hypothermia to cool her body temperature below the normal 98.6 degrees, according to CNN. Doctors then wanted to slow circulation in order to prevent the death of brain cells and, thus, brain damage, caused by prolonged lack of oxygen.

Then, officials told CNN, medical personnel used chilled blankets, then a machine, to keep Thornton’s body temperature cool for 48 hours.

Thornton’s cardiologist is doing tests to see what caused the heart attack, and Thornton is expected to have a cardioverter defibrillator implanted into her chest. Meanwhile, Tugman told CNN that, on April 21, “all of a sudden she stopped breathing, her eyes rolled back and all those machines started going off.”

The hospital released a statement that included a quote from Thornton: “I am so mad I missed the concert.”

Click here for CNN’s report.