There is no objective test for Havana syndrome, but being diagnosed with it grants significant financial and non-financial benefits.
https://en.wikipedia.org/wiki/Mad_Gasser_of_Mattoon
(coincidentally, the "Mad Gasser" was also in Illinois).
I only know about this because of Frank Zappa: https://www.youtube.com/watch?v=352dVmsn7y4
https://en.m.wikipedia.org/wiki/Monkey-man_of_Delhi
There is no objective test for Havana syndrome, but being diagnosed with it grants significant financial and non-financial benefits.