What you are describing sounds like PVC's (premature ventricular contractions) they are nervous in origin (OR can be aggravated by GERD/heartburn) - I've been getting them for about 25 years. Sometimes they come once or twice a day, sometimes not at all, sometimes every few minutes. You get them when you stand up, that is because you are focusing on it AT THAT TIME. They came back for me when I'd go outside and pick up a snow shovel! I could go to the gym, I could do high impact aerobics, I get nothing at all, but the minute I'd walk outside and touch a snow shovel I'd get it because I'd think, "This is when it always happens!" OR if I got to a certain point on the path (shoveling) I'd get it! If you feel your pulse you will feel 2 quick beats, a pause then a hard beat. Is this what you are feeling? Your heart isn't really skipping, it's just that 2 were close together so your heart takes a little break before the next one. COMMON, BENIGN condition.