Different etiologies can have the same symptoms and it is silly to suggest there is no difference between diseases. They’ve found tests which can distinguish long Covid.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10292739/#:~:te....
Because exercise alone can weaken the immune system enough to Reactivate viruses.
There are some conditions this doesn't apply to, but it was good advice for me.
"EBV has also been implicated in several other diseases, including Burkitt's lymphoma,[58] hemophagocytic lymphohistiocytosis,[59] Hodgkin's lymphoma,[60] stomach cancer,[12][61] nasopharyngeal carcinoma,[62] multiple sclerosis,[15][16][63][17] and lymphomatoid granulomatosis.[64]"
Burkitt's lymphoma is an oddball cancer in which growth is so fast treatment should begin almost immediately.
Frankly, I’m expecting a huge rise in the rate of Early onset Alzheimer’s.
Differential diagnosis is important because treatment may be different depending on the underlying problem.
[1] https://nap.nationalacademies.org/read/27756/chapter/7#186