Why is it that i get lightheaded while standing up?

Several reasons: Light headedness when going from a sitting to a standing position is called orthostatic hypotension and may be the result of a sudden drop of blood pressure when you stand and the blood flow to the brain is diminished for a very short period of time. It could be related to taking blood pressure medication or it may be due to the fact that in general, your blood pressure is low. See your doctor.