I have a pretty bad startle reflex/response. I experience it over pretty mundane things - sudden movements of any kind, 'shadows' out of the corner of my eyes, sudden noises (loud or small), loud ongoing noises, kid noises (I have a kid, she unintentionally startles me quite a lot). Sometimes I jump badly, sometimes I only startle slightly. I'm very easily startled when anxious, feeling confused or depersonalised, or in deep thought. I often scream or yell in a freaked-out way.
I feel an instantaneous sense of feeling wildly out of control, panicky, scared that something bad has happened, terrified that I'm unsafe; usually followed by pretty intense and irrational anger. I often have an immediate instinct to defend myself fiercely, fight back, and often shout angrily at the person or thing that caused me to startle.
Immediately following often explosive rage is usually deep, deep humiliation, which furthers my anger. Takes me a while to calm down from.
I can never laugh it off. It triggers me much too deeply for me to be able to think coherently or to make decisions. I am simply in utter primal reactive mode when startled.
I've got it a bit better under control than I used to. I have developed enough self-restraint that I no longer shout or get angry with my daughter if she startles me. That's a big step for me because I otherwise find it very hard to control the irrational rage I experience immediately following being startled.
My startle reflexes and responses have gotten worse over the years. My ex, whom I currently lives with, loves to play jokes and prank around, and thinks it's hilarious to startle me and then watch me get angry. He sometimes will antagonise my anger, then blame me for being "too out of control". Well, what do you expect, you dickhead. You startled me, which you know I can't handle well, then you provoke my instinctive anger response, then call me names when I react angrily to you provoking me. That's like provoking a lion, then punishing the lion for getting angry and aggravated by the provocation.
I seem to have gone on a ranting tangent! My apologies!