Don't start worrying, especially after reading some of this, its probably nothing at all to worry about, for instance most of my life I have had what some people call palpitations which are actually extra beats (from the specialists mouth) and also fast heartbeat, which sometimes would stop me sleeping, I have had tests etc and they found a slight abnormality which they told me not to worry about and it wouldn't effect anything, and I have been relatively healthy.
Now due to being bothered by the fast heartbeat again I have now been put on beata blockers to even out and slow my heartbeat, and now its fine, the only thing that seems to make it fast again is too much sugar.
So bottom line make an appointment to see your doctor.