Startle response is a two part process, firstly it is about no longer fearing your traumatic experience and secondly exposure therapy is what helps change the startle response.

You must consider certain things though in this equation. Firstly, it is actually normal to startle if frightened instantly. What would not be considered normal, is anything beyond what one would classify as "normal" in a startle response, ie. hitting the floor is not normal, jumping of the ground is not normal, etc. A startle is classified as a short shock to your system... anything beyond that short shock is what you would tackle through exposure therapy and ensure your fear of certain responses is dealt with.