to be in the middle of a major emergency. i felt like i was having a heart attack. first tee to the 18th. felt like i was going to pass out. i didn t have a choice. reporter: the stakes were huge. his future on the pga tour, his livelihood on the line. i told my caddie we are not leaving here unless i am getting carted off middle of the fair way. reporter: no sooner did he finish than the ambulance whisked him away. doctors determined his heart was healthy. turns out he was having a panic attack. the sudden onset of extreme anxiety causing the body to pump out adrenaline as the fight or flight response kicks in. the heart racing uncontrollably, sweating, shortness of breath. 6 million americans suffer from panic disorders. symptoms that are similar to having a heart attack. and people fear that they are dying. reporter: under the circumstances, it s remarkable that he finished the round. in fact, only later from his hospital bed did he discover how well he did.