I had a really bad pounding heart episode once, which i went to the doctor about and they did a heart test on me (name of which has gone out my head - they wired me up to this machine... what is it called?? Its something like a ECM or something!?!?)
They were being overly cautious cos of the diabetes (as usual, surprise surprise) and i was fine. But it was really nice to get my mind put at ease, so if it's worrying you go see your doc.
However - I still sometimes get it at night or when i'm anxious. The doctor said caffiene can be a big cause!