Just a few minutes ago, I was sitting and calmly browsing the web when all of a sudden my heart started pounding. I felt it in my chest and a little bit in my throat. It felt as if my heart was about to burst out of my chest. The accelerated heartbeat only lasted a couple seconds. I wasn't dizzy afterwards, nor did I have trouble breathing so it wasn't a heart palpitation. It wasn't painful either. Anyone have any ideas on what it could be?