"Schizophrenics who experience tactile hallucinations of pricking or of 'electric shocks' jump when they feel an injection of ethyl chloride or a real electric shock: 'That time,' they say to the doctor, 'you are the cause of it, because you are going to operate'" (p 389).
So the individual themselves know well the difference between their hallucinations and reality. Again:
"Another schizophrenic, who said he could see a man standing in the garden beneath his window, and pointed to the spot, giving a description of the man's clothes and general bearing, was astonished when someone was actually placed in the garden at the spot in question, wearing the same clothes and in the same posture. He looked carefully, and exclaimed: 'Yes, there is someone there, but it's someone else.' He would not admit to there being two men in the garden." (p 389)
Merleau-Ponty concludes:
"Hallucinations are played out on a stage different from that of the perceived world, and are in a way super-imposed upon it..... The fact that a hallucination does not take place in the stable and intersubjective world means that it lacks fullness, the inner articulation which makes the real thing reside 'in itself', and act and exist by itself." (p 395)
DSM adherents and psychiatric relativists would do well to dispose of their own personal, arbitrary notions of psychology - which Freud derided many in his day of having - and read the actual literature that exists on the subject.