Postural hypotension is considered a failure of the cardiovascular system or nervous system to react appropriately to sudden changes. Normally, when you stand up, some blood pools in your lower extremities. Uncorrected, this would cause your blood pressure to fall. But your body normally compensates by sending messages to your heart to beat faster and to your blood vessels to constrict. This offsets the drop in blood pressure. If this does not happen, or happens too slowly, postural hypotension results and can lead to fainting.

James, Paul A.; Oparil, Suzanne; Carter, Barry L.; Cushman, William C.; Dennison-Himmelfarb, Cheryl; Handler, Joel; Lackland, Daniel T.; Lefevre, Michael L.; MacKenzie, Thomas D.; Ogedegbe, Olugbenga; Smith, Sidney C.; Svetkey, Laura P.; Taler, Sandra J.; Townsend, Raymond R.; Wright, Jackson T.; Narva, Andrew S.; Ortiz, Eduardo (18 December 2013). "2014 Evidence-Based Guideline for the Management of High Blood Pressure in Adults". JAMA. 311 (5): 507–20. doi:10.1001/jama.2013.284427. PMID 24352797.
John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.
Some people have blood vessels that are stiff and lack elasticity, due to vascular disease. When this affects the tiny arteries (arterioles), the arteriolar stiffness causes increased resistance to the flow of blood and high blood pressure. This is most common in people who are also obese, have a lack of physical activity or exercise, have high salt intake, and are older.
^ Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents, National Heart, Lung, and Blood Institute (Dec 2011). "Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents: summary report". Pediatrics. 128 Suppl 5: S213–56. doi:10.1542/peds.2009-2107C. PMC 4536582. PMID 22084329.
The guidelines also say that a patient's blood pressure levels should be based on an average of two to three readings on at least two different occasions. It's also reasonable for doctors to screen for "white-coat hypertension," which occurs when blood pressure is elevated in a medical setting but not in everyday life, the authors said. This can be done by having patients measure their blood pressure at home. 
Pulmonary hypertension is caused by changes in the cells that line the pulmonary arteries. These changes cause the walls of the arteries to become stiff and thick, extra tissue may also form. This can reduce or block blood flow through the blood vessels. Increased blood pressure is then caused because it is harder for blood to flow. Pulmonary hypertension can be an associated condition with scleroderma, sarcoidosis, pulmonary embolism, and dermatomyositis.

There are even more medication types that can lower blood pressure. Some of these are alpha blockers, vasodilators, and central alpha agonists. Your doctor may prescribe these medications if other medications have been ineffective or if you have another condition along with hypertension. Side effects can include fast pulse, palpitations, dizziness, diarrhea, or headaches.
"Blood pressure guidelines are not updated at regular intervals. Instead, they are changed when sufficient new evidence suggests the old ones weren't accurate or relevant anymore," says Dr. Paul Conlin, an endocrinologist with Harvard-affiliated VA Boston Healthcare System and Brigham and Women's Hospital. "The goal now with the new guidelines is to help people address high blood pressure — and the problems that may accompany it like heart attack and stroke — much earlier."
Some high blood pressure medications initially cause drowsiness, dizziness, and lightheadedness. Some even cause fainting on the first dose. The body usually adjusts to the effects of these medications and the side effects disappear. Consuming alcohol during the early phase of antihypertensive treatment could be risky because alcohol can also cause dizziness, drowsiness, and lightheadedness. 

Facial flushing: Facial flushing occurs when blood vessels in the face dilate. It can occur unpredictably or in response to certain triggers such as sun exposure, cold weather, spicy foods, wind, hot drinks and skin-care products. Facial flushing can also occur with emotional stress, exposure to heat or hot water, alcohol consumption and exercise — all of which can raise blood pressure temporarily. While facial flushing may occur while your blood pressure is higher than usual, high blood pressure is not the cause of facial flushing.  
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