I have reported one such case that occurred in Oxford… The patient, a 43-year-old man, was brought into the Accident and Emergency Department following an overdose. He had tried to kill himself because he was afraid he was going to be “locked up”. However, this fear was secondary to a paranoid system at the heart of which was the hypochondriacal delusion that he was “mentally ill”.
He was seen by the duty psychiatrist and by the consultant psychiatrist on call, neither of whom were in any doubt that he was deluded. Indeed, both were ready on the strength of their diagnosis to admit him as an involuntary patient.
(cited from Mind Hacks: This delusion is false)
This very interesting text would be important reading on the topic of reality billing by itself, but it requires some further elaboration.
The only way out of this logical issue is to assume that the concept of delusion has no relation to truth or falsehood. In fact, a delusion might turn out to be actually true, for example, jealousy-induced delusions are more than others likely to be true. In turn, the obvious conclusion from that, that delusion is based on consensus, is not exactly true, or at least, doesn’t tell as much as it should.
The concept of delusion is based on reality, and reality, the way humans actually see it and use it, has a lot to do with consensus, based both on the physical underpinnings and agreement required to actually communicate and divide labor. “To have a delusion” means to exist in a reality that is significantly incompatible with the dominant one, but not just any such reality — only ones living in which results in harmful physical consequences due to incompatibilities should be considered delusions.