You are experiencing PVC's or PAC's.
Premature atrial contractions (PAC)
vs Premature ventricular contractions (PVC)
Those two only differ in their originating form. One comes form the atrial area of your heart and the other from your (you guessed it) Ventricular.
These happen to all people at one point of their lives. Some just feel them more frequently then others. Some are more sensitive to them than others aswell.
you are an unlikely candidate for heart disease. But I'll tell you what, to ease your mind and put your anxiety to ease, go to your doctor and insist for a cardio to check you out.
ECG, Holter, and Stress test, I guarantee you nothing is wrong with your heart. Its a cause of your anxiety disorder. You can't stop them from happening, however you can limit drinking/caffeine and other drugs.
On the other hand, if you are fainting, feeling dizzy (as not a result of anxiety tricking you) or are trying to catch your breath (besides having a panic attack from them) consult your doc.
And finally, as to why you are feeling this so called "Skip".
When you heart pumps blood in reality all is suppose to go smoothly "beat, beat, beat, beat, etc"
However when you have a PAC, or a PVC, you're heart PREMATURLY "beats" before its suppose to, usually this is associated due to the electrical system in your heart. However in people with PVC, or PACS your heart fires before it should, there for, as your heart "resets" your vessels and compartments fill up with blood, when your heart fires back up it usually feels "Stronger" and this is why you feel the sensation of a "flipflop" or "skip"
Hopefully that'll put your mind at ease.