There is no real danger, but problems can stem from an inexperienced hypnotist who acts irresponsibly when with a subject who is in a trance. It is up to the hypnotist to make sure the environment and setting are safe and that the subject is not overlooked after the trance has ended. It is the responsibility of the hypnotist to make sure that the subject is wide awake and has not been negatively impacted by any suggestive commands given while under a trance.
Should a subject become disoriented, feel overly sleepy after the trance, suffer headaches and eye strain, or become less responsive to outside stimulus, more attention must be given to the subject.
If such an occasion should occur, it is important that the subject is immediately placed under trance again and be redirected into a deep sleep. While under a deep sleep, a hypnotist should command them to wake up feeling refreshed and to let go of all previous trance commands. By practicing safe and responsible hypnosis and making sure that your subject is taken care of, all things should be fine. And if you are unable to get the person who placed you into a trance to help you, you should find another hypnotist to help put you back into this deep trance-like sleep and release you from previous commands.