Chill, I've had that before, especially when I use my vaporiser-usually happens if you do too much too quickly. Just chill, listen to music, watch a film, it'll pass. Doesn't have to be anything to do with paranoia/polluting your lungs-the whole idea of a vaporiser is that you don't.

It happens because the weed lowers your blood pressure, so your heart has to work harder to pump the blood around. Happens in all of us to some degree when we smoke, most of the time we just don't notice.