When a person is lying down, the pressure in the blood vessels of the legs decreases, the sympathetic nerve excitability decreases, the regulation of the heart contraction force is weakened, the blood vessel contraction force decreases, and the blood pressure decreases slightly. However, if the blood pressure is lowered too much, it may be caused by disease, and requires hospitalization to clarify the cause of the disease and treatment. When a person is standing, the blood is affected by gravity, the pressure in the blood vessels of the lower limbs increases, in order to protect the blood supply to the brain, to avoid excessive blood in the blood vessels of the lower limbs, the blood returning to the heart decreases, the sympathetic excitability rises, the heart’s contractile force increases, the vascular constriction force rises, and the blood pressure rises slightly. It is recommended to choose a sitting position when measuring blood pressure, in a quiet environment, hands should be relaxed on the table, back should be leaning on the back of the chair, legs naturally hanging down on the ground, do not cross, do not talk during the measurement. If lying down to measure the blood pressure decreased significantly, may be caused by prone syndrome, common in pregnant women, lying on the back of the uterus pressed the inferior vena cava, making the return of blood volume decreased, resulting in a drop in blood pressure, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, for targeted treatment.