I think the term flu-like is often used in lists of symptoms of PEM, along with other common symptoms and reduced function. That's the version for formal clinical use.
Another way it is used is in metaphors trying to convey the impact of PEM, where a pwME describe PEM as feeling like a combination of flu, hangover, and having run a marathon. Hit by a truck, sat on by an elephant and other colurful images are somtimes used to convey being forced to lie still in the dark feeling extremely awful.
If we want a very brief few words for PEM, I might just say feeling very ill and can't function.
Another way it is used is in metaphors trying to convey the impact of PEM, where a pwME describe PEM as feeling like a combination of flu, hangover, and having run a marathon. Hit by a truck, sat on by an elephant and other colurful images are somtimes used to convey being forced to lie still in the dark feeling extremely awful.
If we want a very brief few words for PEM, I might just say feeling very ill and can't function.