As people age, they get plaque buildup inside the blood vessels, and the flexible walls of the arteries become stiff. Now, when the heart squeezes and pushes the blood out, the blood vessels can't expand like they used to do and sustain higher pressure. Over time, the heart has to push so hard against the pressure that it starts to fail, Bauman said.
The symptoms similar to symptoms of patients with hypertensive crisis are discussed in medieval Persian medical texts in the chapter of "fullness disease".[155] The symptoms include headache, heaviness in the head, sluggish movements, general redness and warm to touch feel of the body, prominent, distended and tense vessels, fullness of the pulse, distension of the skin, coloured and dense urine, loss of appetite, weak eyesight, impairment of thinking, yawning, drowsiness, vascular rupture, and hemorrhagic stroke.[156] Fullness disease was presumed to be due to an excessive amount of blood within the blood vessels.
As for when to check your blood pressure, the most important thing is to do it consistently the same time of the day (ask the doctor which time he prefers and also what time in relation to taking your medication). The following article has a lot of good information for someone just starting to monitor their blood pressure:
^ Jump up to: a b c d e f Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo Jr. JL, Jones DW, Materson BJ, Oparil S, Wright Jr. JT, Roccella EJ, et al. (December 2003). "Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure". Hypertension. Joint National Committee On Prevention. 42 (6): 1206–52. doi:10.1161/01.HYP.0000107251.49515.c2. PMID 14656957. Archived from the original on 20 May 2012. Retrieved 1 January 2012.
High blood pressure is classified as either primary (essential) high blood pressure or secondary high blood pressure.[5] About 90–95% of cases are primary, defined as high blood pressure due to nonspecific lifestyle and genetic factors.[5][6] Lifestyle factors that increase the risk include excess salt in the diet, excess body weight, smoking, and alcohol use.[1][5] The remaining 5–10% of cases are categorized as secondary high blood pressure, defined as high blood pressure due to an identifiable cause, such as chronic kidney disease, narrowing of the kidney arteries, an endocrine disorder, or the use of birth control pills.[5]
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.
About This Image: Chart showing potential causes of low blood pressure The risk of low and high blood pressure commonly increases as a person ages due in part to changes during the aging process. The flow of blood to a person's heart muscle and brain declines as a person ages, many times as a result of plaque buildup in their blood vessels. Approximately 10-20% of people over the age of 65 experience postural hypotension. While the causes of low blood pressure may not always be clear, it might be associated with things such as:

Postural hypotension is considered to be a failure of a person's cardiovascular system or nervous system to react appropriately to sudden changes. Usually, when a person stands up, some of their blood pools in their lower extremities. If this remains uncorrected, it would cause the person's blood pressure to fall or decrease. A person's body usually compensates by sending messages to their heart to beat faster and to their blood vessels to constrict, offsetting the drop in blood pressure. If this does not happen, or does not happen quickly enough, postural hypotension is the result.
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).
Physical examination may include listening to the heart and lungs, feeling for pulse in the wrist and ankles, and feeling and listening to the abdomen looking for signs of an enlarged aorta. The examiner may also listen in the neck for carotid bruits (sounds made by a narrowed artery in the neck) and in the abdomen for bruits made by an abdominal aortic aneurysm.
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).                                                                                                                                                                                                
A blood pressure reading contains two numbers: systolic pressure and diastolic pressure. Systolic pressure is the top or first number in your blood pressure reading; it indicates the pressure within your arteries when your heart pumps out blood. Diastolic pressure is the bottom number, and shows the pressure in your arteries while your heart is filling with blood.
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.
An exception to this is those with very high blood pressure readings especially when there is poor organ function.[79] Initial assessment of the hypertensive people should include a complete history and physical examination. With the availability of 24-hour ambulatory blood pressure monitors and home blood pressure machines, the importance of not wrongly diagnosing those who have white coat hypertension has led to a change in protocols. In the United Kingdom, current best practice is to follow up a single raised clinic reading with ambulatory measurement, or less ideally with home blood pressure monitoring over the course of 7 days.[79] The United States Preventive Services Task Force also recommends getting measurements outside of the healthcare environment.[80] Pseudohypertension in the elderly or noncompressibility artery syndrome may also require consideration. This condition is believed to be due to calcification of the arteries resulting in abnormally high blood pressure readings with a blood pressure cuff while intra arterial measurements of blood pressure are normal.[81] Orthostatic hypertension is when blood pressure increases upon standing.[82]
With low blood pressure, the patient may feel faint or lose consciousness. This is due to lack of blood flow to the brain, and usually laying the patient supine will help them come round. This is also known as a blackout, and it could be accompanied by a dizzy feeling and light-headedness. Generally, your patient will report trouble focusing, difficulty keeping upright and lack of coordination.