An elderly patient complains of dizziness and light-headedness when he stands up after lying down. explain the cardiovascular response that may be involved in this case

Blood pressure tends to drop markedly when a person goes from lying down to a standing posture. This is due to blood typically pooling in the lower extremities during a stand, lowering the blood flow to the brain. When the brain loses this flow, dizziness and lightheadedness can result. However, the blood vessels usually constrict and the heart rate typically increases, rapidly returning BP to a normal state.