Hypnosis has been prevalent for thousands of years and successfully used by Doctors, Dentists, Health Professionals and a whole host of famous names including, Sir Winston Churchill, Albert Einstein, Mozart, Robbie Williams, Bruce Willis, Matt Damon, Sylvester Stallone, Kevin Costner, Tiger Woods ; Royalty members ; Prince Harry, Kate Middleton, Fergie and princess Di. ( To name but a few )
Back in 1955, The British Medical Association gave a report endorsing hypnosis as a valuable medical tool. Since then there have been many more recommendations by authorities such as the Health Education Authority and the Media such as the New Scientist Magazine.
Hypnosis is a perfectly natural state in all human beings and animals, as natural as perhaps breathing. You will have passed into hypnosis many times a day, without realising. It happens when you are totally absorbed with something and your focus of mental attention  is drawn inwards. It is a form of daydreaming; allowing direct communication with your subconscious mind and beneficial for building confidence ; to accept change more readily and to encourage better beliefs and attitudes.
It is extremely relaxing and contrary to popular belief you are under nobody’s control except your own. You are not fast asleep whilst under going hypnosis, and you will be aware of things that are going on around you.
To explain how it works, without getting too ultra complicated, it can be best described as a matter of habits, subconscious mind and brain waves.
All of your habits, good bad or indifferent are stored in your subconscious mind. Over time you will have learnt them, and with constant repetition and reinforcement you will have made them a part of you. They will now be guiding you on autopilot as it were.
It has been scientifically proven that during hypnosis the dominant brain waves are the therapeutic theta waves, which are directly linked to increased material synthesis in the brain; which in turn is linked to new learning. So in effect what you are doing during is breaking apart, old out-dated habits, and creating new more beneficial ones.
( A form of mind reprogramming)
Another important feature about hypnosis is the fact that various parts of the mind become naturally more active and other parts tend to take a back seat. This acts as a form of reconciliation and cleansing of unwanted habits, so essentially you are will be over writing an old programme.
All this proves a very valuable psychological point that imagination and habit ( subconscious mind ) will win over strength and will power ( conscious mind ) every time as the conscious part of the mind, is in relation, only a small part of your total mind.