Remember how after watching an episode of your favourite soap you could tell someone what happened although you wouldn't remember the episode word for word, well the same can be said for a session of hypnotherapy.
The vast majority of people remember the session, but not word for word, although sometimes some people will have such a lovely time in hypnosis that they drift off and can't remember everything. This will only happen if you are totally secure and feel comfortable with your hypnotherapist as all of us have an inbuilt "guardian of the gate" that will allow acceptable suggestions through to the subconscious as well as sound the alarm if an unreasonable suggestion is made, the unreasonable suggestion being rejected.
If you fall asleep, and I explain to all of my clients not to go to sleep, of course you won't remember anything and none of the suggestions would take effect. Sleep is not hypnosis, it is nothing to do with hypnosis, and it's far cheaper to have a nap at home than to pay me to sleep in my chair for an hour! Any good, skilled hypnotherapist will of course ensure that you do not go to sleep anyway.
The whole point of a good hypnosis session is to bring about the positive changes that you want to make and therefore the main point of everything is to not necessarily remember the whole session but to ensure that the words and advice given by the hypnotherapist brings the result that you want. The words become actions. You stop smoking, you lose weight or you feel good about yourself again.
If you want to remember one thing, remember this, BE HAPPY.
Dave.