I suppose some 'always been healthy' people can't understand invisible illnesses.
Maybe we need to make T-shirts with Sayings On them, or ball caps.
"Its Neurological"...that might be a good one.
"Orthostatic Intolerance Joy"
"I Fall Over Easily, do You?"
"Eppstein Barr Ate my Collagen"
Or: for more recent new recruits: "COVID GOT ME"