One risk of hypnosis is after emerging from the trance. The person may not have completely ‘recovered’ from the hypnotized state. If he drives his car back after the session while still in half daze, there is a possibility of a car accident.
It is like you just wake up after a night’s sleep, and goes right ahead to drive your car. Your mind is still in a drowsy state and is not able to focus well. That is the danger! Of course, accident may not necessarily occur as a result but it does increase the possibility of you getting into danger.