There is no such thing as “subconscious mind.” The subconscious, or unconscious mind, is a theory—not a part of your brain. Hypnosis is not a magic pill (though it can feel like it.) It is not being controlled, it’s not being in a coma, nor is it being made to do embarrassing things (stage hypnosis.) It is not unnatural, it’s not dark arts, nor is it pseudo-science.
We learn. We make connections. We make habits out of some of those connections. That process happens much faster in a “suggestible” state of mind. Hypnosis Motivation Institute, the school I studied at, describes Hypnosis, in terms of suggestibility, as one of the ways we learn. Hypnosis is natural. It seems to be a state of hyper focus, like watching a movie, or reading a book, in which your mind is focused on something at the exclusion of all else around.
Though attracting research interest from institutions around the world (even the CIA) the actual mechanism of hypnosis is disputed. Suffice it to say, Hypnosis and Self-hypnosis are normal mechanisms. In fact hypnotist Dave Elman, known for teaching dentists how to use hypnosis as an alternative to medication, refers to himself as a hypno-operator, a guy that pushes the buttons on your hypnosis mechanism.
“The sub-conscious” refers to that which has been automated. You’ve probably noticed how easily bad habits form. If you look into it you’ll find that much of what you do during the day, how you interact with people, how you eat, what and when you eat, what you feel, even what you say and think are often habits. Even worry itself can be a habit! When you do anything repeatedly the brain makes a habit of it. Neurons that fire together—wire together. They become coated with a protein, a sort of insulator, called myelin making the neurons more efficient. You no longer need to "think" about doing whatever it is those neurons are wired to do. You can see it happening here.
So why can’t you make a habit out of being thin? Or not smoking? Or being rich? You can, However the myelin sheathing around an earlier habit acts like resistance to change. The process of Hypnotherapy, and to a lesser extent self-hypnosis, expose those old habits and their triggers along with the underlying associations. Together we devise a new behavior, one you can accept, in increments you can accept. then turn on your hypnosis mechanism and create a new, healthier habit. Sounds over-simple? It is. Probably why so may Psychologists are learning hypnosis.