If your systolic and diastolic blood pressure are in two different categories, doctors consider the number that is in the higher category. For example, if your blood pressure is 135/91, your systolic blood pressure is in the prehypertensive range and your diastolic blood pressure is in the range of Stage 1 hypertension. Your measurement or 135/91 would place you in the category of Stage 1 hypertension.
Health issues may happen; however, when a person's blood pressure suddenly drops and their brain is deprived of an adequate blood supply. The condition may lead to lightheadedness or dizziness. A sudden drop in blood pressure usually happens in a person who has risen from a prone or sitting position to a standing one. When this occurs it is referred to as, 'orthostatic hypotension,' or, 'postural hypotension.' Another type of low blood pressure may happen when a person stands for extended periods of time; it is referred to as, 'neurally mediated hypotension.'
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Another form of postural hypotension occurs typically in young healthy individuals. After prolonged standing, the individual's heart rate and blood pressure drop, causing dizziness, nausea, and often fainting. In these individuals, the autonomic nervous system wrongly responds to prolonged standing by directing the heart to slow down and the veins to dilate thereby removing blood from circulating in the arteries.
Blood pressure fluctuates throughout the day, so measuring it in the morning might yield a different number than, say, the afternoon. Conditions like stress and lack of sleep can also fluctuate blood pressure. Visiting your doctor might feel nerve-wracking, which can elevate your blood pressure and create a condition called white coat hypertension.

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.
^ Jump up to: a b Daskalopoulou, Stella S.; Rabi, Doreen M.; Zarnke, Kelly B.; Dasgupta, Kaberi; Nerenberg, Kara; Cloutier, Lyne; Gelfer, Mark; Lamarre-Cliche, Maxime; Milot, Alain (2015-01-01). "The 2015 Canadian Hypertension Education Program Recommendations for Blood Pressure Measurement, Diagnosis, Assessment of Risk, Prevention, and Treatment of Hypertension". Canadian Journal of Cardiology. 31 (5): 549–68. doi:10.1016/j.cjca.2015.02.016. PMID 25936483.
If your blood pressure is above the normal range for up to 5 readings (taken at different visits), your doctor will likely diagnose you with high blood pressure. Sometimes the doctor may diagnose you after a fewer number of readings, depending on how high above normal your blood pressure is and if you have other medical conditions. Blood pressure tends to be at its highest during exercise, physical work, or stress, and lowest during sleep. Everyone can have a temporary increase in blood pressure at one time or another, which is why it's important to take multiple readings.
A blood pressure reading measures both the systolic and diastolic forces, with the systolic pressure listed first. The numbers show your pressure in units of millimeters of mercury (mm Hg)—how high the pressure inside your arteries would be able to raise a column of mercury. For example, a reading of 120/80 mm Hg means a systolic pressure of 120 mm Hg and diastolic pressure of 80 mm Hg.
With age, comes an increased risk for systolic hypertension which can be aggravated by severe atherosclerosis. According to one study, the diuretic chlorthalidone (Hygroton) had significant benefit in elderly patients with systolic hypertension. Along with a diuretic, some calcium channel blockers, ACE inhibitors and angiotensin II receptor blockers may also be good choices. However, beta blockers may not be as effective for hypertension in those over 60; though they may be good choices if co-existing heart disease is present. It also may be preferable in elderly patients to give two high blood pressure medications at a low dose versus one at a higher dose.
An electrocardiogram is known by the acronyms "ECG" or "EKG" more commonly used for this non-invasive procedure to record the electrical activity of the heart. An EKG generally is performed as part of a routine physical exam, part of a cardiac exercise stress test, or part of the evaluation of symptoms. Symptoms evaluated include palpitations, fainting, shortness of breath, dizziness, fainting, or chest pain.
High blood pressure is more common in older people. At age 45, more men have hypertension than women. By age 65, this is reversed and more women are affected. People with diabetes have a greater risk of hypertension than those without diabetes. Having a close family member with high blood pressure also increases your risk of developing it. About 60% of all people with diabetes also have hypertension.
Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure symptoms tend to be more upfront and easily recognizable. The development of symptoms is often a warning sign of a potentially serious underlying disorder. Generally speaking, your blood pressure would need to fall pretty dramatically before symptoms develop.