Hypnos supplied the root for one of the most consequential borrowings any minor Greek god ever received, and the story of that borrowing includes its own inventor's second thoughts. In 1841 the Manchester surgeon James Braid began investigating the trance states induced by so called mesmerists, and in his 1843 treatise Neurypnology he coined neuro hypnotism, soon shortened by common use to hypnotism and hypnosis, deliberately invoking the god of sleep because the induced state outwardly resembled sleep. Braid came to regret the name almost as soon as it caught on, arguing in his later writing that the condition he studied was not true sleep at all but a state of highly focused attention, and he proposed alternative terms, most notably monoideism, meaning fixation on a single idea, to replace the misleading borrowing. The public and the medical profession kept his original word regardless, and Hypnos has named the practice ever since, an outcome the coiner himself spent his later career trying, unsuccessfully, to correct.
The mismatch Braid identified still shapes how the phenomenon is discussed: contemporary research on hypnosis generally treats it as an altered state of attention and suggestibility rather than sleep in any physiological sense, closer in some respects to focused daydreaming than to slumber, so that the ancient god of unconsciousness lends his name to a practice increasingly understood as a state of heightened, rather than diminished, mental engagement.