I'm 19 years old and I made the mistake of playing around with a stethoscope and listening to my heartbeat. About 2 or 3 minutes into listening to it, I heard what sounds like my heart making an extra beat within one beat (lub lub dub instead of lub dub). One time there were a few extra within the beat. This does not show up if you simply feel my pulse. There's not the normal pause I get from the "skipped" beat caused by your heart resetting. It just puts those extra beat or more in and keeps going. I used to have "skipped" beats A LOT when I was younger, and now I only get one or two occasionally, but they're usually more "dramatic" and can knock the breath out of me (no passing out/pain/dizziness though).
My mom heard the extra beats too, so it's not something I was just hearing. They're more apparent when I'm sitting down and leaning over slightly. It also seems to be possibly related to adrenaline/possible hyperventilation. Should I be concerned? We're also calling my doctor in a couple of days.