Hypnosis cannot exist without suggestion. The suggestion, made during hypnosis, bypasses the conscious and is retained in the subconscious where it is acted on later by the conscious (if successful)



Also, Freud did use hypnosis, claiming at the time it was the best means of accessing the subconscious, but he stopped when he was less successful than other hypnotists of his time. Much is attributed to his shyness. During his time, it was thought that a hypnotist had to be a commanding figure. Freud was shy, and even conducted analysis out of the sight of his clients most of the time.

Auto suggestion, by definition, is Self Hypnosis, although many also include Affirmations under the Auto Suggestion catagory as well. In that case, self hypnosis is much more "powerful" and typically much faster than affirmations.

hypnosis is suggestion with the help of hypnotic trance to make the patient easier to imagine and sense what the hypnotherapist is suggesting.

Hypnosis works by directly accessing the unconscious reactive memory system whilst in an alpha or theta brain wave state.
Many people are still well aware of the environment around them during trance work but are deeply suggestible because of the way a proficient hypnotherapist has set the seen. Auto-suggestion / auto-hypnosis occurs simply when your understanding of the process allows you to give direct instruction to your reactive memory with some authority.

So in reality there is no difference between so called hypnotic trance states and auto-hypnotic suggestion. They both work.
Most people find a therapist easier to work with.