Very interesting question, and I will try to find a more succinct answer as I travel the internet.

Basically, however, hypnosis will not "work" for those who really don't want it to, or who really don't "believe" in it. Often, if you want it to work, it will. You generally remain in control, that is, no suggestion can be given that would "work" for you if it was against your own moral or ethical code. (for example, if you are not a violent person, hypnosis will not cause you to do something violent.) Don't confuse hypnotherapy with brainwashing though. They are very different. Whether you remember a hypnosis session or not is up to you, and your ability to assimilate the information you dealt with...often telling yourself you wish to remember will allow it. Make sure, in the USA, that you use a hypnotherapist, or a therapist certified in hypnotherapy. Hypnotists often are not skilled in negative materiel and how to handle it.

Perhaps it is the general "unstableness" of psychosis that prevents a positive outcome from hypnosis? Perhaps they have found that with those who are psychotic, it triggers a psychotic episode? I don't know. Aussies must have a reason for taking such a position!