A hypertensive emergency, unlike the similar sounding hypertensive urgency, is characterized by serious, life-threatening complications. A hypertensive emergency means that the blood pressure is >180 mm Hg or the diastolic pressure is >120 mm Hg, and that end-organ damage is occurring. Signs and symptoms can include shortness of breath, anxiety, chest pain, irregular heart rate, confusion, or fainting. 
When blood pressure is not sufficient to deliver enough blood to the organs of the body, the organs do not work properly and can be temporarily or permanently damaged. Symptoms of low blood pressure caused by conditions or diseases depend upon the specific cause of the low blood pressure. For example, if insufficient blood flows to the brain, brain cells do not receive enough oxygen and nutrients, and a person can feel lightheaded, dizzy, or even faint.
As you age, prevention becomes even more important. Systolic pressure tends to creep up once you’re older than 50, and it’s far more important in predicting the risk of coronary heart disease and other conditions. Certain health conditions, such as diabetes and kidney disease, may also play a role. Talk to your doctor about how you can manage your overall health to help prevent the onset of 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.'
The new guidelines also encourage additional monitoring, using a wearable digital monitor that continually takes blood pressure readings as you go about your life, or checked with your own cuff at home. This additional monitoring can help to tease out masked hypertension (when the blood pressure is normal in our office, but high the rest of the time) or white coat hypertension (when the blood pressure is high in our office, but normal the rest of the time). There are clear, helpful directions for setting patients up with a home blood pressure monitor, including a recommendation to give people specific instructions on when not to check blood pressure (within 30 minutes of smoking, drinking coffee, or exercising) and how to take a measurement correctly (seated comfortably, using the correct size cuff). The home blood pressure cuff should first be validated (checked in the office, for accuracy).
Blood pressure is measured with a blood pressure cuff (sphygmomanometer). This may be done using a stethoscope and a cuff and gauge or by an automatic machine. It is a routine part of the physical examination and one of the vital signs often recorded for a patient visit. Other vital signs include pulse rate, respiratory rate (breathing rate), temperature, and weight.
Enlarged heart. High blood pressure increases the amount of work for your heart. Like any heavily exercised muscle in your body, your heart grows bigger (enlarges) to handle the extra workload. The bigger your heart is, the more it demands oxygen-rich blood but the less able it is to maintain proper blood flow. As a result, you feel weak and tired and are not able to exercise or perform physical activities. Without treatment, your heart failure will only get worse.
Methyldopa, formerly known under the brand name Aldomet, is one of the oldest blood pressure medications still in use. It was first introduced more than 50 years ago. Methyldopa works in the central nervous system to lower blood pressure. While its general use has declined over the years, methyldopa is considered the first-line of treatment for high blood pressure that develops during pregnancy.
Dietary changes: The health care provider might recommend a diet that includes more vegetables (especially leafy green vegetables), fruits, low-fat dairy products, and fiber-rich foods, and fewer carbohydrates, fats, processed foods, and sugary drinks. He or she also might recommend preparing low-sodium dishes and not adding salt to foods. Watch out for foods with lots of hidden salt (like bread, sandwiches, pizza, and many restaurant and fast-food options).

Dr. Rachel Bond, associate director of the Women's Heart Health Program at Lenox Hill Hospital in New York City, who was not involved with the guidelines, said she agreed with the new updates. "I believe this will allow for earlier detection [of high blood pressure], and allow for more lifestyle modification to prevent the long-term detrimental effects of untreated high blood pressure," Bond said.
Low blood pressure is also known as hypotension. This is usually defined in an adult as a systolic recording of less than 90 mmHg, although it has been suggested that for elderly people, below 110 mmHg is a more appropriate definition. Blood pressure and heart rate are controlled by the autonomic nervous system (the nervous system that controls bodily functions that we do not have to think about).                                                                                                                                                                                                
Diuretics can lead to an increase in potassium loss, known as hypokalemia, which, in turn can affect muscular function -- including the muscles of the heart. There is also an increased risk for gout with diuretics -- as well as the possibility of weakness, thirst, dehydration, and increased urination. Changes in blood sugar levels are also possible. Skin reactions, some severe, are possible with thiazide diuretics (such as hydrochlorothiazide). Potassium-sparing diuretics, such as spironolactone (Aldactone) may cause breast enlargement in males.
Historically the treatment for what was called the "hard pulse disease" consisted in reducing the quantity of blood by bloodletting or the application of leeches.[152] This was advocated by The Yellow Emperor of China, Cornelius Celsus, Galen, and Hippocrates.[152] The therapeutic approach for the treatment of hard pulse disease included changes in lifestyle (staying away from anger and sexual intercourse) and dietary program for patients (avoiding the consumption of wine, meat, and pastries, reducing the volume of food in a meal, maintaining a low-energy diet and the dietary usage of spinach and vinegar).
Pulse pressure (the difference between systolic and diastolic blood pressure) is frequently increased in older people with hypertension. This can mean that systolic pressure is abnormally high, but diastolic pressure may be normal or low a condition termed isolated systolic hypertension.[59] The high pulse pressure in elderly people with hypertension or isolated systolic hypertension is explained by increased arterial stiffness, which typically accompanies aging and may be exacerbated by high blood pressure.[60]
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.
Primary (or essential) hypertension is when the cause is unknown. The majority of hypertension cases are primary. When there is an underlying problem such as kidney disease or hormonal disorders that can cause hypertension, it is called secondary hypertension. When it is possible to correct the underlying cause, high blood pressure usually improves and may even return to normal.
Peter, I’ve been using a blood pressure meter for nearly 30 years, so my response is based on my personal experience and information I’ve acquired over the years. First, I suggest that you take your meter to the doctor and have them check several readings of your meter against theirs. For example, If your meter consistently shows it’s 10 points lower than the doctor’s, just delete the 10 points from your meter reading (have them check both numbers so you can adjust both as necessary). Also, it’s common that many doctor’s offices take your blood pressure incorrectly (you should actually sit still for 5 minutes, with your feet on the floor and the cuff at the same level as your heart) . Some of us have”white coat” hypertension, so you may always be elevated at the doctor’s office. If you are a large man, you (and your doctor’s office) may need to use a larger cuff as the wrong size of cuff can affect your reading. Also, I spoke with customer service at one of the companies that makes many of the home & professional meters, and she told me that the automated machines are not very accurate if you have kidney disease or heart failure (I have both). Ask the doctor’s staff to always use the manual system and it will be more accurate than those noisy automatic ones.
Pre-eclampsia is a serious condition of the second half of pregnancy and following delivery characterised by increased blood pressure and the presence of protein in the urine.[23] It occurs in about 5% of pregnancies and is responsible for approximately 16% of all maternal deaths globally.[23] Pre-eclampsia also doubles the risk of death of the baby around the time of birth.[23] Usually there are no symptoms in pre-eclampsia and it is detected by routine screening. When symptoms of pre-eclampsia occur the most common are headache, visual disturbance (often "flashing lights"), vomiting, pain over the stomach, and swelling. Pre-eclampsia can occasionally progress to a life-threatening condition called eclampsia, which is a hypertensive emergency and has several serious complications including vision loss, brain swelling, seizures, kidney failure, pulmonary edema, and disseminated intravascular coagulation (a blood clotting disorder).[23][31]

It's tough to get a reading on your average blood pressure if you only measure it at the doctor's office. Buy a home monitoring kit at your local pharmacy. Take two readings a day, morning and night, for a few days. Repeat these steps a few times a year, and share the results with your doctor. Better understanding of your blood pressure is the first step to preventing heart disease and stroke.

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]
Normal blood pressure is below 120/80. New guidelines from the American Heart Association (AHA) and the American College of Cardiology (ACC) published in November of 2017 consider blood pressure elevated between 120/80 and 129/80. High blood pressure or hypertension is now classified as stage 1 if your systolic reading falls between 130 and 139 or your diastolic reading is between 80 and 89. A measure of 140/90 or higher is now considered stage 2 hypertension. A hypertensive crisis is defined as a systolic rate over 180 or a diastolic rate above 120. An elevated blood pressure means that the heart must work harder to pump blood. High blood pressure can also damage the walls of the arteries. Over time, hypertension increases the risk of heart disease, kidney disease, and stroke. It is estimated that one in three adults in America are affected by hypertension.
Blood pressure readings fall into four general categories, ranging from normal to stage 2 high blood pressure (hypertension). The level of your blood pressure determines what kind of treatment you may need. To get an accurate blood pressure measurement, your doctor should evaluate your readings based on the average of two or more blood pressure readings at three or more office visits.