Well... im not a doctor (nor anything remotely related), but i think the results of hypnotherapy depends heavily on how much you can give up control and allow yourself to be "controlled" by the hypnotist. As more influence you let they have upon you, more effective the results should be. There are even reports of people that underwent surgery without any actual anesthesia, but only under the hypnotists command to be free from any pain.

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"Everything we do, everything we are, rests on our personal power. If we have enough of it, one word uttered to us might be sufficient to change the course of our lives. But if we don't have enough personal power, the most magnificent piece of wisdom can be revealed to us and that revelation won't make a damn bit of difference." Don Juan Matus - Tales of Power