If I have hypnotherapy, will I lose control or be under the control of the hypnotherapist?

When you are hypnotized it's much like being in a meditative state, the only difference is that the therapist is the one helping you get to that relaxed state, much like a guided meditation. But at any state you can just open your eyes. Some states are deeper, but there is nothing a person will do or be controlled to that he or she would not do without being hypnotized.
Also, there is a big difference between stage hypnosis and clinical hypnosis. If you volunteer to go on stage and play along, you will be a perfect subject whether hypnotized or not.
In a clinical, therapeutic environment, we only work with positive and healthy changes and mindset. Who doesn't like that.

Loss of control is not a common experience at all when in regression. If nervousness or anxiousness should come into play, we are trained to reassure the client that all is well and have them rise above that emotional state; to be an observer of what is happening instead of re-living it. Regression therapists are trained to watch the body, the rate of breathing, facial expressions, etc. to monitor the client in every way to insure that they are emotionally and physically comfortable throughout the session.

Even though one is in a deep state of relaxation, as was stated by Sandy, we have to have your willing consent to conduct our procedure from beginning to end. You are always 'aware' of what is taking place on either a conscious or a subconscious level. The subconscious is extremely protective of the incarnated Soul , being the Higher Self who is guiding this incarnated person to evolve. I record and give a copy to all of my clients so that, along with other reasons for recording, it is proof of exactly what has transpired during the session.

It's important to remember that all hypnosis is self-hypnosis... in other words, without your active and willing consent, it's not possible to be hypnotized. That said, find out from your hypnotherapist how they conceive of their role in terms of their relationship to you.

For example, my role as a hypnotherapist is to provide a safe and sacred place for my clients to access another state of consciousness for the express purpose of greater self-awareness, self-exploration, and self-healing. The only agenda I have is to show them the power they have inside themselves. This is why I always give the post-hypnotic suggestion that my client will remember everything that happened while they were in trance, once they are fully awake and conscious.

If you aren't satisfied with how your hypnotherapist describes their role to you, then keep looking for a hypnotherapist who does. Also, ask to record your session so that you can listen back to the entire session to ensure you're satisfied with everything that happened. Finally, I've written an article about Hypnosis Myths that provides more info, it's linked below. Good luck!

A legitimate hypnotherapist would never try to get someone to do something against their values or wishes. As Dylan said above, the loss of control scenario is fiction. In stage shows people are doing silly things and believing silly things because they are comfortable being silly. If someone tried to have them something against their beliefs they would come out of the trance. In my practice all suggestions are carefully designed with the client so they are only getting the suggestions they want for the issues they want to address.