I am the same exact way. I have been experiencing panic/anxiety attacks for a little more than a year. It is one of the scariest feelings in the world when u think something is wrong with ur heart. I experience heart palpitations very often. I am constantly wondering if I am going to die, but the doctor keeps reassuring me that my heart is healthy, & I am absolutely fine.
To answer ur question, yes, a great deal of stress, can cause a heart attack, but I do not think u have anything to worry about at age 21. Obeisity, is also a factor in heart disease, but again, if ur doctor has assured u that ur heart is healthy, then my advice is to take his word. When u feel that ur heart is skipping a beat, remember ur conversations with ur doctor. If u need immediate reassurance, visit the ER, most likely, they will give u something to calm you, & then send u home. I've been there & done that MANY times.
A pshycotheropist would probably give u the stregnth to over come ur anxiety attacks on ur own. I am just beginning to self cope myself. Sometimes, I wonder if I suffer from hypocondriocis.
Also, be sure to ask ur health professional about any prescription drugs that can help u overcome ur fears. I hate being prescribed meds, but I was taking .05 mg of xanax 3x per day, & you'd be suprised at how much it helped me. It was a little expensive though, so my doctor suggested klonopin. 1mg, 2 tx per day. It works great as well. I suggest u discuss ur options with ur doctor, & see if that helps.
Panic attacks r by far the most scary things I have ever experienced, & sometimes, they r hard to get through. However, It sounds to me like u r experiencing the same problem. Just keep eating healthy & I think u will be just fine. I hope u can find something to help u cope with this disorder. No one should have to live their life in fear.
If u ever need reassurance u can email me. jessicamay0120.com. I have found that talking with others with the same problem is one thing that always made me feel more comfortable. Try not to think about it, that only makes things worse. Remember, many people have this disorder, & u will be ok, & hopefully someday be able to overcome these attacks all together! Good luck with everything & take care!