If, during self hypnosis, any interruptions occur which require your immediate attention you can easily regain complete awareness, attend to whatever it is and return to the session again afterwards.
When you have completed your self hypnosis you can easily awaken by counting yourself up again from one to ten. When you reach ten you will be awake and fully aware.
Alternatively, if you are practising self hypnosis before going to bed, you can complete your session by telling yourself you can now fall asleep and then let yourself naturally drift off.