Hi guys. It's my first post here so I hope this is an appropriate topic. I guess you guys would know more about this topic and google doesn't help, so I was looking for advice.

I've been having these scary episodes about twice a month or so, beginning last year. My symptoms during these episodes are basically heart palpitations (fast, pounding heartbeat that doesn't calm down no matter what), heart flutters, and body jolts (I'm zapped awake by what feels like a rush of adrenaline while trying to sleep during an episode.) 

These episodes last for hours, and one felt like it kept going for two days. I almost called 911. 

I feel paranoid that I'll have a heart attack and die, or that my heart is atrophying slowly and it's compensating and I'll die in the next year. I try to calm myself down, distract myself, pray, etc but it doesn't seem to work until my heart decides to chill out hours later.

The thing is, I'm hesitant to say it's a heart condition because I just turned 21, and I'm a healthy weight and good blood pressure and all. I'm also hesitant to call it anxiety because I don't show many of the social symptoms like worrying, low self esteem, or avoiding confrontation. I'm pretty confident in myself and my ability. The only thing I'm not confident in is, well, my heart health because of these episodes I get.

I guess my question is, can someone start having physical panic attacks without the mental anxiety symptoms? And should I take any actions about this?

*I will add, I'm an engineering student and I put myself through a lot of stress due to workload and lack of sleep. But I feel overall happy and am able to have some free time still.