I have this fear that i will get a heart attack its stuck in my mind my cholesterol and everything is fine is it all in my brain? please help how do i get out of this health anxiety?

Very few 18 year olds have a heart attack. If you can not get this idea out of your mind, see a psychiatrist. In the meantime, get some exercise, try to meditate on a positive thought, find a way to help someone else, and find something else to focus your attention on even if it is a videogame.

If reassurance from your primary physician alone is not helpful, you need to seek the help and counselling from a psychologist or psychiatrist. Constant anxiety is clearly harmful in any individual. Please get help.