When you go from lying down or sitting to standing, gravity pulls the blood in your veins towards your legs and the blood is 'pooled' there. This results in less blood returning to your heart (since they are pooled in your veins) and less blood being pumped out of your heart into your arteries. This causes a decrease in your arterial blood pressure (the dizzy feeling) which is quickly sensed by baroreceptors in your carotid artery.
The barorecepotrs direct the brain to increase sympathetic stimulation in order to return your blood pressure and the blood being pumped out of your heart to normal. Your heart will pump harder and beat faster (to get more blood into circulation). Your blood vessels will constrict (increase blood pressure and increase venous return to the heart). These responses all return blood pressure to normal.
One way to quickly stop feeling dizzy is to move your legs after you stand up. Contraction of the muscles in you legs help the venous blood return to your heart faster.
The barorecepotrs direct the brain to increase sympathetic stimulation in order to return your blood pressure and the blood being pumped out of your heart to normal. Your heart will pump harder and beat faster (to get more blood into circulation). Your blood vessels will constrict (increase blood pressure and increase venous return to the heart). These responses all return blood pressure to normal.
One way to quickly stop feeling dizzy is to move your legs after you stand up. Contraction of the muscles in you legs help the venous blood return to your heart faster.
Source:
Physiology (2nd ed.) by Linda S. Costanzo
Physiology (2nd ed.) by Linda S. Costanzo
