I had brochitis as a child, which by adolescence and several years of treatment with inhaled steroids seemingly just settled into an adulthood of "I wheeze and my lungs just don't work well". Never saw anyone about it, just figured it was my lot.

In 2012 I had a really bad lung infection that resulted in an asthma-like attack and ambulance taking me to hospital in the middle of the night. Months of tests resulted in them diagnosing me with Small Airways Disease, which my layman brain recalls as meaning "your big pipes are fine, but your thousands of small pipes are terrible". Not much to be done medically, but they were astonished that I had at that point run a couple of half marathons and essentially prescribed "keep running!". My readings when keeping a peak flow diary were "lungs of an 80-85yo female", rather than the 35-40yo male I was. That's pretty bad: https://patient.azureedge.net/media/Default/_Profiles/4e4362...

At the end of 2016 I had reason to visit my surgery's nurse about another matter and she said "can I hear a wheeze?". A few tests later, and (apparently) some kind of threshold for one of the measurements has changed in the last few years, and hey presto: I'm officially asthmatic.