It's probably down to anxiety.. I get this too more on a night time when I'm trying to sleep and once I feel it in my chest it is hard for it to go away.. I suffer from anxiety so maybe this is another symptom.. I wouldn't worry to much if its beating its doing what its meant to do.. But I know that's its scary and you think the worse but don't.. If you get so concerned and what some peace of mind ring up your doctor and ask him/her for some advice.. But ifyou don't want to you can check loads of anxiety symptoms on here and see if you fall under any of them hope I helped..
