Howard Bloom who famously had CFS for decades talked about how he had a bad flu that never got better and his long recovery from it.
https://medicalerrorinterviews.podbean.com/e/howard-bloom-pa...
Michael J Fox who famously has Parkinson's mentioned being sick in his documentary "Still" while filming "Leo and Me" where other crew members also have Parkinsons: https://en.wikipedia.org/wiki/Leo_and_Me
https://www.michaeljfox.org/grant/h5n1-influenza-virus-etiol...
Many people who are suffering with Long Covid CFS are more obvious though. The significant event from their pre/post covid life was a covid infection.
It is beyond me how people can deny post viral syndromes. Just about every major virus has documented literature of people suffering. Long covid is putting a flashlight on a real problem. For those more interested in the journey, see https://www.youtube.com/watch?v=VYNMzaZk_iU for a great overview.