The failure to properly diagnose my asthma ultimately cost me a good portion of my career. I was well in to my 40s before my allergies (ragweed and a mold called alternaria) and asthma were properly diagnosed.
Both ragweed and alternaria peak in the fall. Every year I would hit a point in cross country season when my performances just fell off a cliff. I'm certain it cost me at least a state cross country title in high school. I was walking through races and was had lost just once to someone not in our state class. At the state meet, I moved in to the lead for the first time at the halfway point and thought the races was over. Within a 100 meters, I couldn't breathe and drifted back to tenth. After the race, my legs were blue and there's no doubt now that I had an asthma attack.
I college, I had a number of similar experiences. I would start the season in great shape, then by mid-late October (when ragweed and alternaria are both in full bloom), I would just fall apart. By late November (after a freeze had taken them out), I'd be back to normal. I never understood it and wreaked havoc on my confidence.
But I never knew any of that. Now, properly treated, I sail through running in the fall. I learned years later that my doctor had told my parents that I had "asthmatic bronchitis" when I was a kid and that I would "probably grow out of it." Needless to say, I didn't. What I wouldn't give to be able to roll back the clock and be able to get some of those cross country seasons back and be able to breathe throughout the season.