Hypnosis (from the Greek hypnos, "sleep") is often thought to be "a trance-like state that resembles sleep but is induced by a person whose suggestions are readily accepted by the subject." Basically, putting someone into a hypnotic trance and accessing untapped areas of their unconscious mind.
The technique is sometimes used for medical purposes to relieve anxiety, or otherwise improve or alter behaviour. Its effectiveness has been clinically demonstrated in many areas, most notably in the area of acute pain relief. It is also used in popular stage acts in which subjects are persuaded to perform bizarre feats.
Other variations include so-called "mass-hypnosis," in which crowds are simultaneously influenced, and autosuggestion in which subjects persuade themselves. However, these phenomena are unlike those typically associated with the classical phenomena of hypnosis.
Although we can speak of a "history of hypnosis" prior to the 19th century, it should be clear that the word itself is the invention of 19th century Scottish physician James Braid. It is not clear if what is discussed as hypnosis prior to the 19th century in histories of hypnosis is actually what we mean today by "hypnosis." Early theories on hypnosis are due to Abbe Faria, a Goan priest.
During the Middle Ages and early modern period, hypnosis began to be better understood by physicians such as Avicenna (Ibn Sina).
Franz Mesmer in the 1700s believed that there was a magnetic fluid that surrounds the body. He experimented with magnets to influence this field and so cause healing. He later found that the same effects could be created by waving the hands in front of someones face. One of his students found that a person could be helped into a trance state by doing this. Franz Mesmer is apparently where the word mesmerize originated.
Hypnotic susceptibility is the measurable responsiveness that a person has to hypnosis. About 10% of people are somnambulistic which is what a stage hypnotist looks for. There is little evidence linking susceptibility to intelligence or personality traits, but some research has linked hypnosis to the amount of imagination in subjects. Recent research suggests that highly hypnotizable people have high sensory and perceptual gating abilities that allow them to block some stimuli from awareness.
There is a common claim that no one can be hypnotized against their will. There is no evidence that this is true at all in any way if the conditioning is effective, long-term and undetected. Like TV for example.
