As the others have said, definitely get it checked out - I have this now - I have only had it with this pg and my first, both of which are girls, which is bizarre - both boys I had no issues. I was sent for an ultrasound of my heart about 2 months ago I guess? And it showed that I have a murmur, which I knew, and that it's just fluttering a bit sometimes because of the 30% more blood going through it, combined with the hormones and the heart being squashed upwards with all the other organs. They keep a close eye on me though - I was already a high risk patient, so I have been getting checked for everything weekly.

Chances are it's the same kind of thing - more blood going through, hormones, squished organs. I get dizzy spells with mine too. But best to mention it to your doc and see what they think