Palpitations are the sensation of feeling your heart beat -- it can a be a PVC, sinus rhythm, etc.
If you feel the pause and then the hard beat, it is probably a PAC or PVC. The only way to know for sure is to capture in on a monitor. You can't always tell from the description of symptoms what is going on.
It is hard to tell how long they will last. Some people have them their whole life, others will just have intermittent episodes of them.
I hope this helps. Thanks of r posting.