Hypnotherapy expert, Dr Peter Marshall, former Principal of the London School of Hypnotherapy and Psychotherapy Ltd. and author of A Handbook of Hypnotherapy, devised the Trance Theory of Mental Illness, which provides that people suffering from depression, or certain other kinds of neurosis, are already living in a trance and so the hypnotherapist does not need to induce them, but rather to make them understand this and help lead them out of it.
Ernest Hilgard, who developed the "neodissociation" theory of hypnotism, hypothesized that hypnosis causes the subjects to divide their consciousness voluntarily. One part responds to the hypnotist while the other retains awareness of reality. Hilgard made subjects take an ice water bath. None mentioned the water being cold or feeling pain. Hilgard then asked the subjects to lift their index finger if they felt pain and 70% of the subjects lifted their index finger. This showed that, even though the subjects were listening to the suggestive hypnotist, they still sensed the water's temperature.
Hypnotherapy is guided hypnosis, or a trance-like state of focus and concentration achieved with the help of a clinical hypnotherapist. This trance-like state is similar to being completely absorbed in a book, movie, music, or even one's own thoughts or meditations. In this state, clients can turn their attention completely inward to find and utilize the natural resources deep within themselves that can help them make changes or regain control in certain areas of their life.