Hypnotherapy use the power of your unconscious mind to make changes. 

The word "hypnosis" (from the Greek hypnos, "sleep") is an abbreviation of James Braid's (1841) term "neuro-hypnotism", meaning "sleep of the nervous system".

Hypnotherapy is used to modify a person's behavior, emotional content, and attitudes, as well as a wide range of conditions including dysfunctional habits, anxiety, stress-related illness, pain management, and personal development.

Hypnosis is a relaxed, focused state of concentration.  But the actual state of mind when a person is highly relaxed is an  "Alpha" brain wave state. It has often been referred to as a deep sleep, it is in reality a specific state that the brain enters into when it is receptive to suggestion. This has been discovered on scans during hypnosis. It is not an unusual state of mind, and may feel like you are not in a trance, or in hypnosis. Most people experience a deeply and often profoundly relaxed state. There is a change in the brain wave activity, similar to that time just before sleep when the alpha state is entered. Your brain's waking state is a beta brain wave, just as you are going to sleep it changes to alpha and then to delta and theta in deep sleep. The alpha state is a very dreamy, pleasant state. During this time the mind is very open to visualizations and creating a rich sensory experience. The more real the experience becomes in the subconscious mind during this state, the more effect it will have on your waking behavior. 

The communication with your subconscious is best accepted when symbolism, and experiences are presented rather than just words.