first of all, have you been hypnotized? I have, I've also spent years researching the subject.
no one really knows exactly what hypnotism is but the best explanation is somehow the subject is tricked into acting under the influence of the unconscious mind rather than than the conscious, in the same way a somnambulist will get up in the night, still asleep and go down and raid the fridge for example. he could appear to be 'awake' but have no memory of it the next morning.
the unconscious mind can do anything the conscious mind can do except it does not know what is real and cannot criticise in the same way. this is how stage hypnotists make subjects carry out amusing stunts.
when I was hypnotized I had almost no memory afterwarRAB of what I was made to do which would have been highly embarrassing but I was told afterwarRAB.
the very small part I did remember was like a dream and the hypnotists instructions seemed like my own inner voice rather than someone talking to me, which is how it works.
a subject does not have to believe he is hypnotized because he can be hypnotized covertly in various ways so he does not know it.
once the subject is placed in a trance state the hypnotists commanRAB become the subjects inner voice below the analytical level of the mind. the subject could quite likely break the trance with an extreme suggestion but there are some people who can be made to do anything.
so, if a hypnotized person is told for example, when the music starts you will be a ballet dancer, he will not think I'll belive this because I'm hypnotized because his conscious mind is gone and to his unconscious mind, which cannot criticise, he believes he is a ballet dancer.
I was put in a trance from sleeping by a hypnotist who was able to gain entry to my bedroom and I eventually discovered what happened, so I did not go along with it at all.
this works because when a person is asleep he can still hear but it was nothing like the way derren brown was supposed to have done it, which I'm sure was bogus.
at stage shows I'm sure some participants are not really hypnotized, but some are. obviously they go along with the induction, but once in the deeper stages the mind
can be taken over by the hypnotist.
also there have been cases where a member of the audience hearing the indction, who did not want to take part, started to go under, was spotted by the hypnotist and was made to take part in the show unwillingly.
there are also shock inducttions where a person can be put in a trance without having to believe in it.
as regarRAB my remark about derren browns hypnotism,
from my knowledge of it I've never seem him perform real hypnotism, like for example the american hypnotist Tom Silver, have a look at some of his clips on you tube.