If I were you, I'd go get it checked out by a physician just to be on the safe side. Several years ago, when I started having palpitations, felt tired and weak a lot and had a bit of dizziness a few years ago, I went to my primary doctor. He did an EKG and a Halter Monitor test, which didn't show anything wrong. But he sent me to a cardiologist, who ordered some tests. Eventually, I found out I had mild Aortic Valve Regurgitation and I continue to have followup on that. I was already being treated for high cholesterol. I figure it's better to know what it is than just to wonder and worry. At least I can try to live a healthier lifestyle since I know what causes the symptoms.
There are a variety of reasons for the symptoms you are experiencing including premature atrial or ventricular contractions or an SVT (supraventricular tachycardia) which includes a number of different types (atrial flutter, atiral fibrillation, AVNRT, atrial tachycardia, junctional tachycardia). The first step is to identify what is going on which is often done initially by a standard 12-lead EKG and possibly a holter monitor. These can be performed by your regular primary care physician or a cardiologist. If you are experiencing increased frequency or symptoms (shortness of breath, light-headedness, dizziness, or syncope), it is important that you are evaluated by a physician who can perform a complete history and physical examination to determine what tests are necessary to help make a correct diagnosis for treatment (if needed).
What you're experiencing does indeed sound like the common, harmless extra or 'ectopic' beats that so many of us here write about. The fact that you're young and female also argues for that. That said, it never, ever hurts to see a doc for a basic EKG when you experience symptoms like these for the first time.
The trouble is that in hypersensitive folks, as many of us are, once we become aware of these odd little heartbeats--even if our docs have told us we're fine--we tend to get fixated on our hearts, to the point that we have trouble thinking of anything else.
When that happens, the best thing to do is see a therapist, preferably a shrink (who has had medical training) about anxiety or panic, and short-circuit the whole fingers-on-the-pulse thing. It's possible to lose *decades* of perfectly good life to pointless fears.
You almost certainly are suffering from harmless Premature Atrial Contractions (PAC) or equally harmless Premature Ventricular Contractions (PVC). These phenomenons feel to most people like a skipped beat, a flutter, or a thump. Or, in my case, they feel like the air is sucked out of you for a split second.
Most often, particularly in someone your age, these are caused by things like excess stress, anxiety, caffeine, alcohol, or sugar. They can occasionally be a sign of a more serious problem but that is very rarely the case. A simple visit to a cardiologist should do the trick as they'll run a few test just as a precaution.
It's a fact that worrying about PACs and PVCs will bring them on even more so try and relax first and foremost. These beats are considered normal and almost everyone has them so try not to get stressed out over them and they'll get better.