Flu-like illness

Flu-like illness is a diagnosis when a doctor is not sure of the virus causing a patient's symptoms. Common cold viruses, RSV, parainfluenza, and rhinovirus can cause symptoms similar to the flu. A doctor may think you have the flu but doesn't see the point in doing an official flu test as it won't change what your doctor recommends for symptomatic care.

Flu-like illness in ME/CFS
Many ME/CFS patients had a flu-like illness as their onset. Flu-like symptoms are experienced by all patients no matter the onset/trigger and these symptoms are exacerbated by minor exertion which is called post-exertional malaise.