How would I know that I was hypnotized?
You will know from the results. Did you respond to the suggestions? Did you experience a relaxed state, as suggested? Did the suggested situations / scenes seem realistic? How about the feelings in your body, do you feel any change? Perhaps less heaviness in the shoulders, perhaps breathing is more free, the lump in the throat has gone or the stomach has loosened up. Check your mood and your emotions. How did they change? What about your goal? Do you feel the change?
Sometimes the change from the hypnotic session takes time to occur, and when it does happen it seems you did it yourself. This is basically true, any change you do yourself. The therapist only helps you start it, just gives you a gentle push and helps you to access your internal resources.
If you are not sure, you may ask your therapist for proof. The therapist can give you a specific suggestion. For example, she may suggest you touch your ear any time he talks to you after the session. Or he may even suggest that you will quack like a duck, if it is the proof you asked for…