Hypnotherapy and hypnosis is often referred to as trance work by NLP practitioners. People experience trance states in ordinary, everyday life. Driving along and missing your motorway exit because your mind was someplace else is a common experience of a trance state. We can manufacture trance states at will, ever willed yourself to be someplace else during a boring meeting and found your mind wandered off somewhere entirely different? Well that's trance for you!
Most therapists believe that there is an interpersonal feedback loop that takes place in every experience, it's not as simple as entering an unconscious hypnotic state whilst a therapist issues hypnotic instructions to your mind. A trance state is simply a narrowing of focus.
The good news (and there's only good news because your unconscious mind can only process positive thoughts and commands for your wellbeing, a bit of a self-defense mechanism) is that you have total control over these experiences, so can take charge of your own experience. In modern hypnotherapy the therapist is the facilitator of that positive experience.
Modern hypnosis has been dominated in the 20th Century by the work of Milton Erickson (see History of NLP). He discovered that language was a key factor in hypnotherapy, the subleties of language and how it was used.
This has been the strength of the NLP approach to hypnotherapy and trance work, the use of language being the "Linguistic" part of NLP (Neuro Linguistic Programming). Researched by Richart Bandler and John Grinder, this was put in an accessible form, and is commonly called the Milton Model, being used as a basis for hypnotherapy inductions.
More recently, therapists involved in hypnotherapy and trance work have explored the concept of trance states even further. The phenomenon of hypnotic episodes can generate experiences which feel very real, and may cause daily problems, and these have been created by ourselves. These trance states have been given names, for example "pseudo orientation in time", is when we regularly imagine lots of things going wrong in the future with any undertaking. This results in feeling anxious all the time in the present and avoiding making plans. Another common trance phenomenon is "negative hallucination" when we don't see something that is there, or don't hear something being said. In other words we delete (or filter out) information. Someone overweight, or indeed very underweight, will filter out information that doesn't fit with how they see themselves. So someone with anorexia nervosa won't see a thin person in the mirror, and won't hear comments about their excessive weight loss. This enables them to maintain their problematic behaviour.
Trance states usually come in clusters, several will be present. NLP hypnotherapy techniques use the Milton Model and the application of hypnosis to identify these trance phenomenon and work with them to generate positive alternatives.