Some people experience sudden drop in blood pressure when they stand up from lying or sitting position. This type of low blood pressure is called postural hypertension.
Postural hypertension is a condition when autonomic nervous system (part of nervous system which controls such vitally important involuntary processes as heartbeat) is unable to respond adequately to sudden changes. When you get up, a significant blood volume flows into your lower extremities. This may cause drop in our blood pressure. But, as a rule, your body compensates this drop by sending by sending impulses to heart to make it to beat faster and to blood vessels to make them contract. Thus, pressure drop is neutralized. Postural hypertension develops when this process does not happen or happens too slowly. The risk of high or low pressure is increased with age and is partially associated with the natural process of aging. Moreover, with age blood supply to brain is worsened due to formation of plaques on the walls of vessels.
The pattern of loss of consciousness in patients with postural hypertension is stereotypical. Fainting usually occurs in the way well known by the patient. In such patients the arterial blood pressure is normal in lying position. They usually lose consciousness at night or in the morning right after getting up from the bed. Unlike vasodepressor fainting, loss of consciousness caused by postural hypertension occurs suddenly and without any precursors. After getting into horizontal position, the arterial pressure of the patient increases to the normal level and the patient comes into consciousness.