I had that right after I had my daughter, but it was happening 2 times a minute or 4 times a minute for 4 hours straight! (so that would be 60 to 120 times in 30 minutes!) - that is absolutely anxiety. You may feel it in your throat and it tickles a bit and you have to cough, or you feel it missing a beat and the "pause" kind of takes your breath away, then after the pause the heart beats forcefully. Then the more you worry about it the worse it will get, then you'll get MORE worried and it will get worse, viscous cycle. To put your mind at ease if you went to a doctor they'd give you a 24 hour holter monitor to wear, then he'll see it on the readout, tell you it's anxiety or "cut back on the caffeine" and you'll relax.