I definitely had them during this pregnancy, and I think it might have something to do with the increased heart rate, blood flow and probably stress the body is under.
Definitely mention it as they can check your blood pressure, and if it's happening often or gets worse or painful they could consider monitoring you or doing a heard echo to check your heart. When they happen, make a note of the time and what you were doing and how long it lasted for, and that can help the doctor decide whether it's needing further investigation, as this is what they'll initially tell you to do anyway! Also note if you get dizzy or faint or breathless during them. Try to stay away from caffeine in the meantime as well if you do have things with it (cokes, coffee, lucozades etc).
I'm sure it's nothing to worry about and wouldn't panic about them. I get them all the time, pregnant or not, had my heart fully investigated and there's nothing wrong! As long as they're not painful all it is is your heart trying to regulate its beat. x