Contrary to what you have seen in film and television, Hypnotherapy is not magic! Hypnotherapy is not a magic button, and is in fact a therapy that typically does require more than one session to uncover and create the various desired shifts in behaviors.

Hypnotherapy is NOT mind control.  You are never in a state of being controlled. While in the hypnotic state you are 100% in control of your thoughts and feelings at all times. Even though some of the deeper depths of hypnosis can result in some amnesia after the session, during the session you are completely aware of what is going on at all times. Typically the deeper depths (or somnambulistic depths) are used for things like dental surgery. 

Hypnosis works to replace known associations in the subconscious mind with new ones that are beneficial to the changes you want to make in your life. 

While in the hypnotic state, similar to when you fall asleep, your brain wave activity changes which allows you to become attentive and acutely focused on the suggestions being presented. 
Each suggestion given in the hypnotic state is specially formulated for each client in order to increase the potential for acceptance within the subconscious mind. Everyone's subconscious speaks our own language, thus if the suggestion for change is not presented in a manner that is conducive to your subconscious it may reject the suggestion.

While each person is different in the required amount of sessions,  I strongly recommend a minimum of two visits.  Creating shifts in behavior patterns and gaining an awareness of how to produce desired change(s) are the focal points of the first session.  It is very effective in gathering and garnering momentum while the second session aims to reinforce and further build our foundation as a paradigm shift begins to take place.  From there, we refine and tailor our work to address specific issues that may arise or to simply bolster what we have already learned. The success of hypnosis is a self driven process that requires work from both the client and myself.  

It is not uncommon that after one session a client will feel great.  For others, there can be an apprehension to enter into a hypnotic state so some gentle guiding and a basic of understanding that a hypnotic state is nothing more than a deep state of relaxation is necessary before some feel comfortable letting go.  A good hypnotherapist should do their best to let you know exactly what will transpire as well as what to expect along the way