Image credit: Reinhold Matay/AP Photo

Charlie Beljan came out on top at this weekend's PGA Tour event, but on Friday, during the second round, he suffered a panic attack so severe, he thought he wouldn't be able to finish.

"I thought I was having a heart attack," he told ABC News. "I felt from the first tee to the 18th, I felt like I was going to pass out but I didn't have a choice."

With his future on the PGA tour and his livelihood on the line - he needed to win the tournament to avoid having to requalify for his tour card, Beljan kept the paramedics at bay as he progressed one hole at a time at the Children's Miracle Network Hospitals Classic in Lake Buena Vista, Fla.

"I told the caddy, I said, 'I'm not leaving here until I'm getting carted off from the middle of the fairway or somewhere,'" he said. "I just kept putting one foot in front of the other and I got through the day."

After he finished the round, Beljan was transported by ambulance to a hospital where doctors determined that his heart appeared to be healthy.

Beljan eventually learned that he'd suffered a panic attack or the sudden onset of extreme anxiety.

Extreme anxiety causes the body to pump out adrenalin and epinefren as the body's fight or flight response kicks in. The physical symptoms can be frightening and resemble a heart attack, with the person experiencing heart palpitations, sweating and a shortness of breath.

According to the National Institute of Mental Health, 6 million Americans suffer from panic disorders.

"Most often when people experience panic, they try to escape the situation that they find themselves in," said Dr. Jeffrey Janata, a University Hospitals Case Medical Center psychologist. "He [Beljan,] by virtue of what he was doing, was unable to escape so he had to sort of hang in there while these panic symptoms persisted."

Beljan said on Friday evening, as he lay in a hospital, he realized how well he had managed to play.

"I finally looked at my phone at 10:30 [p.m.] and that's when I realized I had a 3-shot lead," he told ABC News. "It was probably a blessing in disguise because I spent more time worrying about breathing and slowing things down."

Despite the panic attack, Beljan had carded a 64, his second-best round of the year. He played two more rounds during the weekend, not only keeping his panic at bay and forcing himself to stay calm, but also holding off the rest of the field. His 16-under-par 272 gave him his first PGA victory, making him the fourth rookie to win on tour this year.

"It's quite remarkable that he was able to kind of talk himself through it," Janata said, "[and] manage the symptoms cognitively and get through a round and do quite well."

ABC News' David Wright contributed to this article.