Hypnosis is NOT sleep, as often believed. Most people feel very relaxed and may look like they are asleep, but are still at a level of consciousness between the two. This means that you are aware of what is being said and are still capable of communicating if asked to respond and you still have the choice whether to accept the suggestions given or not.
You have complete control throughout this process, and should you wish to open your eyes you will be able to do so. However, the whole experience is relaxing and enjoyable, so that you will most likely not want to.
You will return to full waking consciousness feeling relaxed and refreshed. Often clients feel that they have not been hypnotised as they have been able to recall the all that has been said and their thought processes during. Some clients go into trance easily and only can recall parts of what has been said, but everything has been heard and absorb by their unconscious mind.