Post viral syndromes have existed forever, some of us just have paranoid immune systems. Just about any virus could cause it, or exacerbate it. Things like RSV, the flu, and mono in particular. Perhaps chicken pox for those of us who were pre-vaccine kids. I caught some virus or another a couple times per school year, who knows which one broke the camel’s back.

If we actually had to survive in the wild then the tendency to develop post viral syndromes would have been wiped out quick.
Idiocracy may actually be infectious.