You must have lost all your power, which is when Freddy comes to jumpscare you, and there is nothing you can do about it.
However, you can clutch with this method. if you are having trouble conserving your power throughout the entirety of the night, then you can try and conserve it until a little after 5am. By doing so, you will have a high chance of getting to 6 am and completing the night, before Freddy can jumpscare you.