My heart gets startled a lot faster than ever before, like if my mom calls my name or if a pencil hits the....?

it even gets startled if a pencil hits the floor. I am so scared and even when im sitting, my heart feels a little uncomfortable, like it is ready to get scared again. Im 19 and my mom and my dad are just fine. I dont know if im about to get a heart attack or go through cardiac arrest soon. Like when I didnt get much sleep and i was laying in a movie theatre and i closed my eyes, I purposely opened my eyes and my heart get startled!! Even if I know im opening my eyes and nobody woke me up or anything. My heart used to jump when car alarms went off or when someone said "boo!!" but now anything makes my heart JUMP!! I really dont want to die and I dont want to go through a heart attack or cardiac arrest, someone please help and give me advice. THANKS