pretty freaky when it happens and you don't know what it is.. definitely dump the caffeine and if it's persistent for extended periods (as mine was at one time, making it difficult to relax or concentrate on anything else ) try some brisk exercise, even run up and down the stairs a few times - this forces the heart back into a regular beat pattern and is often enough to get everything back even again. It is caused by the heartbeat being triggered extra times early in the cycle, which in itself disrupts the blood flow to a degree and if it continues for extended periods can cause light headedness and tiredness as a result of the reduced blood flow.
Not a "dangerous" condition, but uncomfortable and unnerving all the same.