I had this one time back at the first Colorado cert a couple of years ago. I did "Fran" in a 2-minute PR of 6 minutes or so (desperately trying not to be 200% of Kelly Moore's time, which was something like 3:20 or less that day).
The combination of major exertion and Colorado thin air (I'm a lowlander) left me coughing periodically for the next 3-4 hours. I wasn't alone . . . seemed like half the room was doing so.
I've worked very hard some times since, but never hard enough to induce that response . . . proving once again that "men will die for points" (or to not get thrashed too badly by Kelly).