- 1 decade agoFavorite Answer
coz when you are lying down, you are not doing work or moving around so you don't need as much oxygen for your muscles as when you are standing up trying do support your body.
as you don't need as much oxygen for your muscles around the body, your heart wouldn't pump as hard/fast so the flow of blood is then reduced, hence the pressure decreases.
and that's why your body temperature drops slightly when you lay down for too long.
just a little background knowledge for you...
oxygen that we breath in combines with haemoglobin in your red blood cells by diffusion in your alveoli. when the heart pumps, red blood cells carry the oxygen molecules around your body for your muscle to respire in order to carry out aerobic respiration.
if there is no oxygen for your muslces to respire, anaerobic respiration would be occurred and would produce lactic acid, which gives you muslce pain.
- graceLv 71 decade ago