Heart palpitations, chest tightness. ive been to the er 5 times in the past, normal ekg, blood tests, and chest x-rays each time. my b type natriuretic peptide is at 15.5 pg/ml. my troponin i sensitivity is at 5 ng/l. should i worry? im 23?

Medical history is very important. Are you using drug or do you have history of anxiety or panic disorder? Based on your age, symptoms and test results, coronary heart disease or structural heart disease (cardiomyopathy, valvular heart disease or congenital heart disease) is very less likely. You should not worry much & stop go to ER. Establishing care with an internist is more important.

It is not feasible to provide an opinion without additional history, physical examination may be some tests. It would be prudent to see your doctor to see if you may be depressed. Depression is treatable. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Drink more water. Wish you good health!