Anyone can develop hypotension, but certain groups of people are more likely to experience it, and there are different types. For instance, orthostatic (positional) hypotension, which occurs when you stand up after sitting or lying down, is more common in older adults. Typically, “your body has certain compensatory mechanisms to prevent your blood pressure from falling when you stand up,” explains Willie Lawrence, MD, an interventional cardiologist at Research Medical Center in Kansas City, Missouri, and a spokesperson for the American Heart Association. But, he adds, “orthostatic hypotension is a problem for some people because these reflexes that should occur, don’t occur.”
In most people with established essential hypertension, increased resistance to blood flow (total peripheral resistance) accounts for the high pressure while cardiac output remains normal.[52] There is evidence that some younger people with prehypertension or 'borderline hypertension' have high cardiac output, an elevated heart rate and normal peripheral resistance, termed hyperkinetic borderline hypertension.[53] These individuals develop the typical features of established essential hypertension in later life as their cardiac output falls and peripheral resistance rises with age.[53] Whether this pattern is typical of all people who ultimately develop hypertension is disputed.[54] The increased peripheral resistance in established hypertension is mainly attributable to structural narrowing of small arteries and arterioles,[55] although a reduction in the number or density of capillaries may also contribute.[56]
The value of routine screening for hypertension in children over the age of 3 years is debated.[90][91] In 2004 the National High Blood Pressure Education Program recommended that children aged 3 years and older have blood pressure measurement at least once at every health care visit[89] and the National Heart, Lung, and Blood Institute and American Academy of Pediatrics made a similar recommendation.[92] However, the American Academy of Family Physicians[93] supports the view of the U.S. Preventive Services Task Force that the available evidence is insufficient to determine the balance of benefits and harms of screening for hypertension in children and adolescents who do not have symptoms.[94]

SOURCES: The Journal of the American Medical Association, May 21, 2003. Aram Chobanian, MD, dean, Boston University School of Medicine and chair of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Claude Lenfant, MD, director of the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health. Edward Roccella, PhD, MPH, coordinator of the National High Blood Pressure Education Program at NHLBI. John Laragh, MD, Cardiovascular Hypertension Center at New York Hospital/Cornell University Medical Center and editor-in-chief of the American Journal of Hypertension. WebMD Medical News: "Diuretics Best for High Blood Pressure."

Normal blood pressure is less than 120/80. Knowing your blood pressure and remembering to check it regularly can help save your life. Choosing healthier, heart-conscious foods, maintaining a healthy weight, getting up and staying active, and managing your stress are great ways to help keep your blood pressure at the level it should be. Learn more about what you can do to help control your blood pressure.
Blood pressure (BP) recordings consist of two numbers. The top one is the systolic blood pressure and relates to the contraction of the left side of the heart and the peak pressure achieved when it pumps blood round the body. The bottom number is the diastolic recording and is the lowest pressure achieved in the circulation; this relates to the relaxation of the heart. Blood pressure is measured in millimetres of mercury (mmHg), e.g. 120/70 mmHg.
One especially important cause of low blood pressure is orthostatic hypotension, which is sometimes referred to as postural hypotension. This happens when blood pressure drops rapidly during changes in body position—usually when changing from sitting to standing—inducing classic signs that the blood pressure is too low, like dizziness, blurry vision, and fainting.

The guidelines also redefined the various categories of hypertension. It eliminated the category of prehypertension, which had been defined as systolic blood pressure of 120 to 139 mm Hg or diastolic pressure (the lower number in a reading) of 80 to 89 mm Hg. Instead, people with those readings are now categorized as having either elevated pressure (120 to 129 systolic and less than 80 diastolic) or Stage 1 hypertension (130 to 139 systolic or 80 to 89 diastolic).

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.
Low blood pressure (hypotension) is pressure so low it causes symptoms or signs due to the low flow of blood through the arteries and veins. When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, and kidney, the organs do not function normally and may be temporarily or permanently damaged.
As you get older, high blood pressure, especially isolated systolic hypertension, is more common and can increase your risk of serious health problems. Treatment, especially if you have other medical conditions, requires ongoing evaluation and discussions with your doctor to strike the best balance of reducing risks and maintaining a good quality of life.