You can't hypnotize anyone against their will . You can't make anyone do anything, say anything or feel anything that they ordinarily wouldn't say, feel or do. If you tell someone to go rob a bank the only way they will do it is if they normally would rob a bank. Hypnosis does not confer any special rights privileges or power on the person who uses these techniques in the appropriate clinical settings. In any relationship between a patient and a clinician the opportunity for corrupting that relationship is vast and that is why the ethical practice of medicine is really what dictates what is ethical with respect to hypnosis.
Hypnosis is clinically useful in almost every aspect of medicine.
You give them a posthypnotic suggestion to control their breathing. Can break minor attacks with this. This can work in adults but is much more effective in children. While in trance state you can teach your patients techniques to self-hypnotize themselves. Any process that has a psychophysiologic relationship where mind and body interact to exacerbate or ameliorate the disease process hypnosis can be used.