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.
After developing a substantial following — “mesmerism” became “the height of fashion” in late 1780s Paris, writes Marchant — Mesmer became the subject of what was essentially the world’s first clinical trial. King Louis XVI pulled together a team of the world’s top scientists, including Benjamin Franklin, who tested mesmerism and found its capacity to “cure” was, essentially, a placebo effect. “Not a shred of evidence exists for any fluid,” Franklin wrote. “The practice … is the art of increasing the imagination by degrees.”
Before long, hypnotism started finding its way into the world of modern medicine. The use of hypnotism in the medical field was made popular by surgeons and physicians like Elliotson and James Esdaille and researchers like James Braid who helped to reveal the biological and physical benefits of hypnotism. According to his writings, Braid began to hear reports concerning various Oriental meditative practices soon after the release of his first publication on hypnotism, Neurypnology (1843). He first discussed some of these oriental practices in a series of articles entitled Magic, Mesmerism, Hypnotism, etc., Historically & Physiologically Considered. He drew analogies between his own practice of hypnotism and various forms of Hindu yoga meditation and other ancient spiritual practices, especially those involving voluntary burial and apparent human hibernation. Braid's interest in these practices stems from his studies of the Dabistān-i Mazāhib, the "School of Religions", an ancient Persian text describing a wide variety of Oriental religious rituals, beliefs, and practices.