All hypnosis is actually self-hypnosis, and is based on a deeply relaxed state of mind and body. In this state your subconscious mind openly receives positive suggestions put forward by the hypnotist. It is important to understand that your sub-conscious mind will reject any information that you are not willing to share. A state of hypnosis is not the same as being asleep, you are totally aware of the entire procedure.
Most people do not realize that we all actually experience a form of hypnosis in our daily lives. People often reach states of trance, for example while day-dreaming. Or have you ever driven somewhere and not really remembered how you got there? Sometimes when you read a book or watch TV your mind goes into a trance-like state.
You should be aware that therapeutic hypnosis is different from the type of hypnosis entertainers perform on stage. Therapeutic hypnosis is carried out to help achieve mental and physical well being or to reach a goal. People are always in control, and will never do anything against their will or core values while in "altered" state.
A good hypnotherapist will be responsive to your needs and explain hypnosis in a way that makes you feel comfortable and ready to proceed.