Hi Girls
The problem you are having is because of your blood pressure. Well sort of.
What happens is that when you are pregnant, your veins and arteries all get bigger and wider in preparation for the increase in blood volume. By about 35 weeks your blood volume has increased by as much as an extra 75%. Because your blood vessels get bigger first this can cause a drop in blood pressure but it also is a little harder to pump blood to your brain. This reduced blood supply to your brain causes you to feel dizzy and on some occasions even faint. Putting your head between your knees is a good way to stop you feeling dizzy. But as long as you can get your head lower than the level of your heart that will also work.