What Causes Palpitations By Excessive Paranoia, Anxiety And Panic Attacks?

Hello. For the past couple of weeks, I've been experiencing weird stuff with my heart. It started when my heart started beating really fast, which I had never experienced before and it freaked me out. I went to the hospital and they did an EKG, blood work, and a sonogram. They found nothing wrong with my heart and ruled it as anxiety. But recently, its been acting up again. Two weeks ago my heart was beating fast enough that I couldn't go to sleep. I was checked out again and they said it was another panic attack. I've also started experiencing chest pains and I've started to have trouble sleeping. Now, my heart is beating again, although it is noticable unless I feel it directly. Is this something to be worried about or just heart palpitations brought on by excessive paranoia, as I have been pretty much thinking about my heart a lot. I am 19, I don't drink, smoke, or do drugs. I eat fruits with every meal and I excercise five days a week.