After studying briefly with Bernheim, Freud pioneered the use of hypnosis as a vehicle for regression and catharsis between about 1885 and 1905. However, he abandoned it in order to develop his own technique of psychoanalysis. Nevertheless in an article published late in his career Freud returned to the subject of hypnotherapy once again, suggesting that it might be necessary to somehow combine the findings of psychoanalysis with the methods of hypnotherapy in order to produce a briefer and more powerful form of treatment. This notion was subsequently developed by other psychotherapists and led to the school of hypnosis which we now call “hypnoanalysis.” Freud’s comments here are more in the manner of a brief description, rather than a definition per se, nevertheless they reveal something of his views on the nature of hypnosis.
It has long been known, though it has only been established beyond all doubt during the last few decades, that it is possible, by certain gentle means, to put people into a quite peculiar mental state very similar to sleep and on that account described as ‘hypnosis.’ […] The hypnotic state exhibits a great variety of gradations. In its lightest degree the hypnotic subject is aware only of something like a slight insensibility, while the most extreme degree, which is marked by special peculiarities, is known as ‘somnambulism’, on account of its resemblance to the natural phenomena of sleep-walking. But hypnosis is in no sense a sleep like our nocturnal sleep or like the sleep produced by drugs. Changes occur in it and mental functions are retained during it which are absent in normal sleep. [Freud, On Psychical Treatment, 1905]