Yeah I have it on and off, usually when I run for a train or something. It's quite scary, but apparently not dangerous. It feels like your heart is stopping and starting and flopping about like a fish in a bucket and jumping into your throat, so not the most pleasant.
Once I had it constantly for 15mins where every heartbeat felt out of rhythm. Internet paranoia to the rescue so I thought I was going into atrial fibrillation and went to A&E, where they see plenty of whey-faced paranoids like me every night
As above, it seems to be mostly stress related (I have really bad anxiety so it ties in with that for me). I'm testing a theory that lots of walking and easy exercise helps, but that's probably just because it helps reduce stress for me or something. I've been told to not worry about it, because that'll just stress me out more and make it worse. Oddly enough, I found listening to metal and other new music that gets me amped up takes my mind off it when I'm powering up a hill to catch the train. I work in sales so it's a bit weird when it happens mid-pitch when you aren't expecting it!