The phenomena that when one stands up and closes his eyes, he feels dizzy is referred as orthostatic hypotension. This happens because when you stand up, blood that should have flowed to your brain fall to other parts of the body due to gravitational pull,in other words, your brain is in a temporary lack of blood condition. The deficiency of blood in the brain contributes to dizziness, or pounding in the head. Some feel that his heart is racing when he stands up after sitting a long time. Under severe circumstances, it can lead to syncope. After sitting for a long time, you should stand up slowly to avoid feeling dizzy. And you need to do more exercices in your daily life. Swimming, jogging, gymnastics can benefit you much. Also, sleeping early and getting up early is good to your health. In addition, in your daily diet, eat more foods rich of protein.