Thunderstorm asthma, perhaps. My understanding is that the pollen absorbs water and bursts into smaller fragments which make asthma worse in people who have issues, and creates issues for people who would normally not have issues.

https://allergyasthmanetwork.org/news/thunderstorm-asthma/

I was in Melbourne when the 2016 event happened, and city hospitals were overwhelmed by emergency admissions. Several people died.