Anxiety causes such fears annoyingly frequently. Sometimes even the opposite. I have a slower than normal heart rate, and my anxiety makes me think its a problem. So I go and check my pulse which is stupid, because the anxiety makes it increase slightly. so when i check and see its wrong, it decreases, which scares me, which increases my heart rate... Well you see where this is going.
The point is, you're definitely not the only one with those problems. Horrible though they may be, I don't think its anything dangerous. Of course, as others have suggested it might be best to get checked just for peace of mind. I did, and that's why I know no matter how scary it gets, im actually okay. Its a big help.