Adverse events resulting from relaxation techniques are uncommon. Rare reports describe basilar or vertebral artery occlusion after yoga postures that put particular strain on the neck. People with poorly controlled cardiovascular disease should avoid progressive muscle relaxation because abdominal tensing can cause the Valsalva response. Patients with a history of psychosis or epilepsy have reportedly had further acute episodes after deep and prolonged meditation.
Ernest Hilgard, who developed the "neodissociation" theory of hypnotism, hypothesized that hypnosis causes the subjects to divide their consciousness voluntarily. One part responds to the hypnotist while the other retains awareness of reality. Hilgard made subjects take an ice water bath. None mentioned the water being cold or feeling pain. Hilgard then asked the subjects to lift their index finger if they felt pain and 70% of the subjects lifted their index finger. This showed that, even though the subjects were listening to the suggestive hypnotist, they still sensed the water's temperature.
Hence, the social constructionism and role-taking theory of hypnosis suggests that individuals are enacting (as opposed to merely playing) a role and that really there is no such thing as a hypnotic trance. A socially constructed relationship is built depending on how much rapport has been established between the "hypnotist" and the subject (see Hawthorne effect, Pygmalion effect, and placebo effect).
Self-hypnosis happens when a person hypnotises oneself, commonly involving the use of autosuggestion. The technique is often used to increase motivation for a diet, to quit smoking, or to reduce stress. People who practise self-hypnosis sometimes require assistance; some people use devices known as mind machines to assist in the process, whereas others use hypnotic recordings.
Barber, Spanos, and Chaves (1974) proposed a nonstate "cognitive-behavioural" theory of hypnosis, similar in some respects to Sarbin's social role-taking theory and building upon the earlier research of Barber. On this model, hypnosis is explained as an extension of ordinary psychological processes like imagination, relaxation, expectation, social compliance, etc. In particular, Barber argued that responses to hypnotic suggestions were mediated by a "positive cognitive set" consisting of positive expectations, attitudes, and motivation. Daniel Araoz subsequently coined the acronym "TEAM" to symbolise the subject's orientation to hypnosis in terms of "trust", "expectation", "attitude", and "motivation".
For several decades Braid's work became more influential abroad than in his own country, except for a handful of followers, most notably Dr. John Milne Bramwell. The eminent neurologist Dr. George Miller Beard took Braid's theories to America. Meanwhile, his works were translated into German by William Thierry Preyer, Professor of Physiology at Jena University. The psychiatrist Albert Moll subsequently continued German research, publishing Hypnotism in 1889. France became the focal point for the study of Braid's ideas after the eminent neurologist Dr. Étienne Eugène Azam translated Braid's last manuscript (On Hypnotism, 1860) into French and presented Braid's research to the French Academy of Sciences. At the request of Azam, Paul Broca, and others, the French Academy of Science, which had investigated Mesmerism in 1784, examined Braid's writings shortly after his death.
Hypnosis is not a psychotherapeutic treatment or a form of psychotherapy, but rather a tool or procedure that helps facilitate various types of therapies and medical or psychological treatments. Only trained health care providers certified in clinical hypnosis can decide, with their patient, if hypnosis should be used along with other treatments. As with psychotherapy, the length of hypnosis treatment varies, depending on the complexity of the problem.