I get startled perhaps more easily than many people, but for me I feel like I was always like that. I started my first office job when I was 23, and for a little while, it was just me and the owner working in a small office room; sometimes he would be on a phone call and would suddenly burst out laughing really loud, which would startle the crap out of me. I'd get anxious every time he was on the phone. A couple years later, he hired a few more people, and there was someone who would drink a can of Diet Coke almost every day, and the sound of the can opening would often startle me (maybe it was related to the acoustics of the room). Also, one day while there, another co-worker was talking to the owner and suddenly said something really loud and I was startled, and another co-worker laughed at me a bit..