Thank you! That will be the other hard part. Finding a way for them to understand that I was too sick to work there because I was being made that sick by working there but that illness wouldn't have prevented me from working in general, which is what the law requires as far as I know. So I wouldn't have been able to take a job as a bike messenger, for example, until after I fully recovered, but I was perfectly able right out of the gate to continue doing the type of work I was doing or any other type of work that wouldn't require above average respiratory exertion.
That's the main reason I left when I did. Reaching a point where I was too sick to do anything at all, even sit up at a computer or stand behind a counter, was inevitable if I stayed and it did reach that point when I requested to go on sick leave for recovery. Thankfully, I was able to recover while on leave in spite of the condition returning when I returned to work again, but no one, including a doctor, can guarantee that the damage being done to my lungs wouldn't eventually be irreparable. Having chronic respiratory issues for the rest of my life wasn't a risk I was willing to take. Certainly not for a job.
I just don't know how to prove that I was sick enough to warrant leaving, especially since what I provided wasn't enough. I considered that short of the doctor's letter, I might present credible documented medical evidence that my diagnosed condition is guaranteed to evolve into a more permanent and/or fatal condition if you don't eliminate the cause (which in this case was my place of work), but I don't know if that would be out of place for something like an unemployment hearing.

