Before I begin, i must say i'm no doctor, but an engineering student, yet my mom is a pediatrician and she told me all this a while back when I had one of my first panic attaks on the matter 2 years back i think. Of course I was telling her "i'm dying....heart attack....." and so on, and she lloked at me and just said: "coke, fat, and not enough sleep".
I see we're in the same boat here since I too have the exact symptoms you describe. I'm 24 and I don't drink coffe, tea, coke (maybe once in a while now), alcohol and I also don't smoke or take any drugs(medicines or illegal ones), yet I still experience the heart skipping a beat. In spite of feeling that the heart is 'skipping' a beat, it is actually beating twice in the time is normally takes for the normal rate to beat once. The reason you feel like it's skipping is because the second beat is much weaker than the first one. basically you get one and a half for the price of one.
I usually get this irregular beat when I'm tired, in the morning and at night. It is actually not a heart problem, but a nervous system one. I get the skips when i feel very tired and it actually seems that I have to concentrate on breathing more than normal (it's like it's not an instinct anymore). I dunno if you notice this or not, or maybe it doesn't happen with you, but my breething gets a little irregular when I'm tired and these weird heart beats happen then. I would say it feels like I literally 'forget to breethe' for a while and when I run out of air, i take a deep breath like I was under water for a whole minute. Weird! If you see a relation between irregular breething and these weird beats, try to just stay in one place and force a constant deep breething rate.
Now, i'm not in the greatest of shapes, I don't exercise and I'm quite a couch potato. I think the main reasons for this heart issue is lack of sleep, using excitants(coffe, coke...all those) and weight. Maybe you're not getting enough sleep at night (8 hours) or maybe you can't rest well because of your bed even though you sit in it for 8 hours. Maybe there's too much light in your room and it keeps waking you up. I know that when I wake up tired i'll just have them. When I wake up tired, no matter how little effort I do, i start to get them. I walk upstairs, i get 'skips'. And they actually continue on an on for a while till I actually 'wake up'.
For example, yesterday I went to the Autoshow and I walked all day between cars and it was really tired by the time I got home. Being stupid as I am, i started playing online computer games till 2 AM and i went to bed all excited from the game and I slept bad. Today I wake up, bend to put on sock and... bam!... 'skips'..the worst I ever had...every 5 normal beats *poof* a good ole' skipper! What was different than any other times? I lacked enough rest. That's why I'm here now searching for stuff on this matter.
About being paranoid, maybe the doc was right
. But then again, i panic too. My mom says I'm paranoid, but it is certainly not a fun feeling that you're about to faint and your life is flashing before your eyes!
I guess my advice would be for you to get a better night's rest (get a comfy mattress, darker room...whatever makes you more comfortable sleeping), and if this is your case too, lose some weight. And no smoking or other excitants
I never went to a doctor about this yet, but in most posts I've seen people that went to the doctor were sent home having discovered nothing wrong.
Now, what I described here is the most common heart rate irregularity out there. There could be other reasons but I think that judging by your age, other reasons are not likely. (again i'm no doctor....thoguh I wanted to be till i first saw my own blood from a scratch and almost fainted
Hope this helps, at least with the panic. Knowing that there are so many people out there with similar problems makes me feel a little better anyway.
P.S. If I have skips in the morning, i noticed that taking a nap in the afternoon (even starting at 11 AM) makes them go away for the rest of the day....So in my opinion, there are 3 important things really: REST, WEIGHT(proper nutrition gives more energy-->healthier nervous system ), and NO EXCITANTS. And sorry for the long post coz btw...staring at a computer screen for long is a damn bad excitant (one of the worst actually...it goes straight to your nervous system and starts bashing it).