Why am I so afraid if other people are not?

I can't tell you exactly what it is because I am afraid you would find a way to scare me with it. But I will say that it was something I saw 5 years ago. When I saw it I couldn't stop screaming, shaking, crying. It was awful. It gave me nightmares. Other people who saw it say "it's just supposed to startle you, you are over reacting". Other people jump, then laugh. I have a frikkin panic attack. But I can't help it, to this day, the very thought of seeing it gets me shaking, gets my heart racing. If it's not so scary to other people, why is it so horrible for me? What is wrong with me that I would react in such a way?