What Causes Skipped Heartbeat And Floating Sensation In Chest?

I am experiencing a weird sensation above the heart location, maybe afib?? Hard to describe, but like maybe a skipped heartbeat and a feeling of a split-second floating sensation in the chest. Is this flip-flopping? am 75, good health, female, bp normal, only take .50 mg thyroid med, nothing else. Been noticing it for a week, off and on. Heart rate is about 77 bpm, regular with a longer space every 15 or 20 beats but not always. I check it on my cel phone monitor.