The human body is a very efficient machine. It uses the heart muscles and arterial muscles to circulate oxygen and nutrients to all areas of the body continuously for normal cellular resperation and the viens carry the metabolic waste including CO2 to their final destination for excretion and exhalation. Under normal circumstances your body does not lay completely still, your muscles in the extremeties constantly contract and this contraction pushes the blood in the viens and the excess ectasticial fluids in the lymph system, lost from the circulatory system, back to the heart for the continual movement. The more oxygen and nutrients required, the more muscle contration that aids the return. When standing erect with your knees locked, you are aiding muscles of the legs and hips from becoming fatigued. However, it also inhibits the muscular contraction needed to insure healthy respiration on the cellular level. The blood begins to pool or collect in interstitial fluid and the body begins to adjust to the issue causing the movement out of homeostasis, or normal function. What actually triggers the passing out or falling out of consciousness is not clearly understood yet. Scientists believe that it is how the human body insures that it will flatten to a prone or supine position...or flat. Left unattended the person will lay and jerk around slightly until regaining consciousness. With no perminant side effects.
i don't get why anyone would want to make themselves faint