There are many research and finding done to hypnosis.
One important finding is the decrease of brain activity on the region that is called Dorsal Anterior Cingulate. This is the part of our brain that controls self-awareness by integrating our emotion, cognitive and sensory input.
It is known that in hypnosis, a person though being aware of its surrounding environment, is not aware of certain bodily reactions. One example is being told to bark like a dog. Even a reticent person can do this without fear of embarassment in the public, when in hypnosis.