As a rule, anyone with average intelligence and who is not suffering from any mental health issue (ie psychosis) and can concentrate will be able to achieve a meditative trance state.
The definition of Hypnotherapy given in the Encyclopedia of Mental Disorders states "Hypnotherapy is a combination of hypnosis and therapeutic intervention. The therapist leads the patient to positive change while the patient is deeply relaxed in a state of heightened suggestibility called trance." Through hypnotherapy we are able to bring the subconscious mind in sync with the conscious mind which immediately resolves the conflict.
According to The Concise Columbia Encyclopedia, "Hypnosis is an altered state of consciousness characterized by focused concentration, similar to that experienced when daydreaming or concentrating and oblivious to distraction. It allows access to the highly suggestible subconscious mind. Research has shown electrical changes in the brain during hypnosis; the brain waves of a hypnotized person are usually different from those of a person in the normal waking state. Most people can be hypnotized, although the ability varies from person to person. Techniques vary but usually involve deep relaxation accompanied by the focusing of the mind."
I wish to stress that nobody can be hypnotised against their will and you are always in control when you are in a state of hypnosis.
FACT: In 1958 the British Medical Association approved hypnotherapy as a valid medical treatment. In 1958 the American Medical Association also approved it.