Do you feel dizzy and lightheadedness on standing up suddenly ? When you stand up, gravity causes blood to pool in the veins of the legs and abdomen. This decreases the blood pressure because there is less blood circulating back in the heart. Low blood flow to the brain causes dizziness. The nervous system quickly increases the heart rate and constrict blood vessels, which then rapidly returns blood pressure to normal.
This decrease in blood pressure is called orthostatic hypotension. Orthostatic hypotension is a form of low blood pressure which occurs when you stand up from sitting or lying position. It may be mild and last for less than a few minutes. This is totally normal and there is nothing to worry about. However, long-lasting orthostatic hypotension can signal more serious problem. This would suggest the blood pressure has dropped and is not recovering. It is important to seek medical help, if this problem persists for long time.
To reduce the dizziness and lightheadedness, get up slowly from a lying to standing position. Sit on the edge of the bed for a while before standing.