During last year’s Dallas Marathon relay, Dwayne Pickens had only 5.2 miles for his segment, and he was confident that he’d breeze through it, considering he’d run eight miles the weekend before. About two miles in, the breathing issues started. He told Runner’s World that it was a cold morning, so he thought the cool air was affecting his lungs and making it more challenging to breathe. The next thing he remembers is waking up in the emergency room, where he found out that, technically, he’d been dead on the course for about two minutes. Although he’d never had any...