I can sure relate to your fear. I have skipped heart beats and they really flame my anxiety to the moon.
In answer to your question, in a structurally normal heart, they are not dangerous at all, they just feel like it and scare the bejeebers out of a person. As to what to take natural that helps them, well, the herb, Hawthorne is terrific.
Another idea, this may sound weird, but it works, see a chiropractor, sometimes certain vertebrae that are mis-aligned can cause the flutters, especially the T-2 to T-4 region of the back.
I can also relate to the heart flutters..I used to get them more until I realized they werent dangerous..I go in spirts with my health worries..lately during routine exams I have been trying meditations for ocd and anxiety..works great..also exercise is helping me..