There is a belief, especially amongst skeptics, that hypnosis is nothing more than gullible people acting out because they want to believe it to be true. There can be an element of this especially in stage hypnosis, however recent research has shown that pretence and trance are closely related and the one leads directly into the other. What starts as ‘acting out’ can rapidly transform into a deep trance state.
Until recently there was no way to confirm whether a hypnotic subject was actually in trance or just pretending and no-one could be completely sure that hypnosis was nothing more than a self-fulfilling prophecy of personal behaviour, however over the last 10 years with the advent of fMRI (Functional MRI) it has been possible to view the actual brain activity of individuals whilst under hypnosis and there are some marked differences between individuals who are hypnotised over those who are pretending.
In addition there are some significant changes in the involuntary processes within the body of a hypnotised subject that conclusively show that hypnosis is an independent, psychological and physiological state with its own set of rules and processes that cannot be faked.
Yes, there are still times when people can be pretending but it is much more likely that the subject is in a deep trance state believing they are pretending.