I really reallyy want to disappear...?

i dont know what is wrong with me. If you care im 18 and a total wreck. My life is horrible and right now i feel like im dying. I think something is seriously wrong with my heart...right now its beating really slow. When i put my hand up to my chest or try to feel my pulse i dont feel anything . I feel like i will just pass out and i keep telling people but no one will listen. I am not unhealthy or overweight or anything but i know somethings not right. Ive been going through a lot lately and i think my heart is giving up...ive been awake all night and cant lay down because i know my heart is beating way too slow and if i stop moving, it'll probably stop :( i had/have anxiety issues but my heart rarely beats fast any more...i think that it is about to just stop...my arm also keeps getting a pain and i know its relatted to my heart and i dont want to go through the pain :( i just want to go away :(