It's a bit of a hot take, but I think there's insufficient understanding of just how much of our everyday health complaints are psychosomatic, and just how much of our mental activity doesn't take place in the brain. An allergy to subsonics is certainly a made-up complaint, the only question being whether it's made up by the brain or the immune system. And the only practical difference between those two is that the brain is more plastic.

If the subject doesn't practise deliberate reprogramming of their mental architecture, it doesn't matter much whether the illness is in the more or less pliable medium, because they don't have the tools to reshape it either way. I guess one could run an experiment by seeing whether it's amenable to talk therapy and categorise the issue that way, but it would still depend a lot on the therapist in question and the subject's willingness to participate.

No, it's a classic nocebo.

There recently was a bit of a scandal in Germany because for years a major government authority has reported levels of "infrasound" from wind turbines far above what was physically plausible. A lot of the fearmongering relied on those numbers - yet it turned out they were due to a calculation error.