Feeling a heartbeat...huh?

So, I am lying in bed last night and I began to feel my heart beating.  Like hard.  I almost felt like I was having an anxiety attack because my heart was pounding and I couldn't stop focusing on it.  I was pretty freaked out, but thought maybe I just had a bad dream or something.

Then I got home from working at the Armory today and sat down in bed to relax a bit.  Right away I felt my damn heartbeat again...like hard!  I don't understand.  I can see my shirt moving every time it beats...and it's weirding me out.