The next major development came from behavioural psychology in American university research. Clark L. Hull (1884–1952), an eminent American psychologist, published the first major compilation of laboratory studies on hypnosis, Hypnosis & Suggestibility (1933), in which he proved that hypnosis and sleep had nothing in common. Hull published many quantitative findings from hypnosis and suggestion experiments and encouraged research by mainstream psychologists. Hull's behavioural psychology interpretation of hypnosis, emphasising conditioned reflexes, rivalled the Freudian psycho-dynamic interpretation which emphasised unconscious transference.
People have been pondering and arguing over hypnosis for more than 200 years, but science has yet to fully explain how it actually happens. We see what a person does under hypnosis, but it isn't clear why he or she does it. This puzzle is really a small piece in a much bigger puzzle: how the human mind works. It's unlikely that scientists will arrive at a definitive explanation of the mind in the foreseeable future, so it's a good bet hypnosis will remain something of a mystery as well.
In conventional hypnosis, you approach the suggestions of the hypnotist, or your own ideas, as if they were reality. If the hypnotist suggests that your tongue has swollen up to twice its size, you'll feel a sensation in your mouth and you may have trouble talking. If the hypnotist suggests that you are drinking a chocolate milkshake, you'll taste the milkshake and feel it cooling your mouth and throat. If the hypnotist suggests that you are afraid, you may feel panicky or start to sweat. But the entire time, you are aware that it's all imaginary. Essentially, you're "playing pretend" on an intense level, as kids do.
Hypnosis is effective in decreasing the fear of cancer treatment reducing pain from and coping with cancer and other chronic conditions. Nausea and other symptoms related to incurable diseases may also be managed with hypnosis. Some practitioners have claimed hypnosis might help boost the immune system of people with cancer. However, according to the American Cancer Society, "available scientific evidence does not support the idea that hypnosis can influence the development or progression of cancer."