yes it happens to me as well.it comes over all of a sudden its not nice

i got this checked out at my last MW appoitment iron and blood pressure was fine,she said that as you get to near the end of your pregnancy u have so much more blood going around your body etc , she said that u need to keep your food levels up so eat something small every 2 hours ,like a cracker toast banana yogurt anything really
also make sure your drinking enought water through out the day

if your blood pressure if normally fine then its prob not that, but get it checked as well as iron