Patient
The fact that the guy was walking round apparently ok after landing and being seen by the paramedic points to it being much more likely it was a panic attack than a heart attack.
As Bad Medicine points out, in the air isn't the place to try and make a diagnosis. If in doubt, assume the worst. As I said, I've been wrong and misdiagnosed a panic attack as a heart attack, probably more than once and thats with the benefit of ECGs etc in the back of an ambulance safely on the ground. All the boxes for a panic attack can be ticked, but all the symptoms are so vague that they could be of anything. Low blood sugar, thats something else that can give panicky symptoms (and before starting another change of direction in the thread, no they haven't got to be diabetic).
Always assume the worst. Sticking a paper bag over someones face probably will help if it is just hyperventilation, but thats assuming the best case diagnosis, not the worst.