Hypnotism puts you into a state of “focused concentration,” during which you’re vaguely aware of your surroundings — you just don’t care about them. There are different stages of hypnosis, some deeper than others. But when you’re in any of them, your imagination is open to suggestion.
The suggestions made to you while you’re hypnotized are part of hypnotherapy. This term, sometimes used interchangeably with hypnotism, simply describes the stuff that is suggested to you while you’re hypnotized to help make you better after the session is over. Often the suggestions are images — picturing your arm going numb, picturing yourself relaxed — rather than orders to “stop hurting.”
Over the years, hypnotism has had a rather seedy reputation. This bad rep can be traced back to the late 18th century, when Franz Mesmer, the guy who introduced hypnotism into medicine, got himself kicked out of France for his fraudulent healing practices. Hypnosis was soon discovered to have genuine healing potential, but it was exploited by enough crackpots and vaudeville magicians to stay associated with superstition and evil for a long time.