Even someone's fits might not be an FND after ruling everything else out. There are atypical presentations of organic diseases we don't have tests for. It's fine to use wastebasket codes as long as the patient understands, but I've also seen doctors lean on certain things really early in notes (eg FNDs) without much consideration, and it's a little much to me.
How does that relate to wastebasket syndromes? At least for the one I have (a migraine variant) -- every single accepted treatment falls in the same basket. Some evidence, but not enough that it's really a good idea to use it. Unless, that is, the syndrome is ruining your life.
And behind this argument that yet more things should be taken off the shelves and regulated, I'll note that the US has one of the most restrictive, patient-unfriendly regulatory atmospheres in the world. It's goddamned ridiculous, pardon my French, that the "solution" to phenylephrine not being a good decongestant would be to regulate it so that it can't be sold without a prescription. Doubly so, in a country with a healthcare industry that's so thoroughly corrupt and dysfunctional that a vast swathe of patients can't afford to even go to a doctor to get whatever tenuous recommendation they may have. (Phenylephrine, by the way, has a number of uses other than decongestion.)
... that was a rant. But this system is truly screwed up, that fact has affected my life quite negatively, and it's annoying that the knee-jerk reaction so many people have is to keep playing along with this completely broken ethical system.
doctors need to be up front with patients about wastebaskets though, and rule out other diagnoses. it's wrong to chalk someone's fits up to FND until you've ruled out epilepsy and other organic causes, for example. and even things like FND are probably "real", we just don't know enough about them yet.