It is important to distinguish between two entirely different things: hypnotic trance induction and hypnotic therapy. The practice of interest here is trance induction only. Deep trance is a profound state of parasympathetic dominance. To achieve it requires great skill of the hypnotist and also practice by the 'inductee' (The light trance of most hypnotic therapy is not at all the same). Trance cannot be practiced as self-help, but is perhaps useful to understand its place in context.
Source: Milton Erickson