There are a lot of myths surrounding hypnosis due to the media.
During hypnosis, you are an active participant in your treatment and fully conscious. Many people are even more alert than usual.
You also have the same amount of control as you typically do and the practitioner cannot make you do anything you don't want to.
According to the American Society of Clinical Hypnosis, while rare, a small percentage of people do go into deep enough trances to have spontaneous amnesia, but most people remember everything from their hypnosis sessions.