What you are describing is what we call symptomatic orthostasis. I'll explain what that means. When we stand up from a sitting or laying position, blood that was hanging out in blood vessels in our abdomen and chest falls towards our feet because of gravity. This means that blood is pulled away from the brain, which happens to need a constant flow of blood for normal function. Our bodies have a natural nervous system response that causes blood vessels in the body to constrict when we stand up making sure that adequate blood gets to the brain. Every time you stand up and feel normal, this nervous system that causes the blood vessel constriction has worked properly. When you feel lightheaded, this means that the brain has lost some of its blood flow. This happens either when the nervous system has not worked properly, or if the blood volume is not adequate.
I suggest that you schedule an appointment to see a primary care physician
. He or she will want to ask you some more detailed questions about these symptoms and perform an exam. Because you have not passes out (yet), your doctor
will likely recommend that you drink more fluids and perhaps add
some salt to your diet (if you can believe that). Good luck.