I suspect that individual/obvious fume events might not be to blame. It's well known that regular low levels of exposure to various chemicals can sensitize people so that the reaction they experience gets worse and worse even though exposure levels remain the same. They can also start to react to other similar substances at levels that don't provoke a reaction at all in unsensitized people.
I managed to accidentally sensitize myself to super glue but fortunately it's easy to avoid. Took awhile to work it out but I used it a lot to build a model planes and spotted a pattern. I'd get mild flu like symptoms a day after use. I didn't get that reaction when I was younger or when using other adhesives.
Dictionary - Definition of sensitization
Chemical sensitization: Evidence suggests that some people may develop health problems characterized by effects such as dizziness, eye and throat irritation, chest tightness, and nasal congestion that appear whenever they are exposed to certain chemicals. People may react to even trace amounts of chemicals to which they have become "sensitized."