Dizziness and off balance

I know it’s normal to have this during pregnancy (especially in the second trimester) I’m 20 weeks today and I walked up a flight of stairs and then bent over to pick something up off the floor.. when I stood back up my head went dizzy. It’s been about 30 minutes and I still feel slightly off balance.. just like my head feels funny a little. Blood pressure and pulse are within normal range. I’m just wondering about possible warning signs to look for that could indicate an emergency and if my baby is getting enough blood flow? Please, no mean comments. I’m a first time mom.