Not sure if its normal lol but ive had this many times and have rang midwife to come out and there never seems to be anything wrong. Very annoying, I had a episode last week where I couldn't stand with out feeling I was going to fall. Im 30w 3d with my lil girl, I already have two boys and never had this problem. You could try your midwife see what she says, my dizziness usually lasts for 2 days. Good luck anyway xxx