You’ll want to be careful when standing or sitting up from lying down, as your blood pressure could be lower than usual. Rising quickly may cause you to feel light-headed or dizzy as your blood pressure drops. This is called postural hypotension, and can be a problem up until your 30th week of pregnancy.
What Causes Postural Hypotension?
There are several reasons you might be feeling dizzy, faint or light-headed. First, hormones like progesterone relax your blood vessels, causing them to be less effective in helping to move blood.
Your blood has thickened with extra plasma and doubled in amount during your pregnancy, which is enough to boggle any circulatory system. Sitting in certain positions or lying on your back can cause your uterus to put pressure on major blood vessels, causing your blood pressure to change when standing.