Here's something off of WebMd I found! http://www.webmd.com/content/article/96/103783.htm

In 90 to 95 percent of high blood pressure cases, the cause is unknown. In fact, you can have high blood pressure for years without knowing it. That's why it's the “silent killer” — it creeps up on you. When the cause is unknown, you have what's called essential or primary hypertension. Factors that may lead to high blood pressure in the remaining 5–10 percent of cases, which are known as secondary hypertension, include: Kidney abnormality A structural abnormality of the aorta (large blood vessel leaving the heart) existing since birth Narrowing of certain arteries These problems can usually be corrected. For example, doctors can repair a narrowed artery that supplies blood to a kidney. Most of these problems can be ruled out by a careful history, a physical examination and a few tests. Special tests are sometimes needed, but you don't usually have to stay in the hospital. How does high blood pressure develop? Your heart pumps blood through the body's arteries. The large arteries that leave your heart taper into smaller arteries called arterioles. The arterioles then taper into smaller vessels called capillaries, which supply oxygen and nutrients to all the organs of your body. The blood then returns to your heart through the veins. Certain nerve impulses cause your arteries to dilate (become larger) or contract (become smaller). If these vessels are wide open, blood can flow through easily. If they're narrow, it's harder for the blood to flow through them, and the pressure inside them increases. Then high blood pressure may occur. When this happens, your heart becomes strained and blood vessels may become damaged. Changes in the vessels that supply blood to your kidneys and brain may cause these organs to be affected. Your heart, brain and kidneys can handle increased pressure for a long time. That's why you can live for years without any symptoms or ill effects. But that doesn't mean it's not hurting you. High blood pressure is a major risk factor for stroke, heart attack, heart failure and kidney failure. What does high blood pressure do to your body? High blood pressure adds to the workload of your heart and arteries. Your heart must pump harder, and the arteries carry blood that's moving under greater pressure. If high blood pressure continues for a long time, your heart and arteries may not work as well as they should. Other body organs may also be affected. There is increased risk of stroke, congestive heart failure, kidney failure and heart attack. When high blood pressure exists with obesity, smoking, high blood cholesterol or diabetes, the risk of heart attack or stroke increases several times. What about low blood pressure? Within certain limits, the lower your blood pressure reading is, the better. In most people, blood pressure isn't too low until it produces symptoms, such as lightheadedness or fainting. In certain disease states, it's possible for blood pressure to be too low. Examples include: Certain nerve or endocrine disorders Prolonged bed rest Decreases in blood volume due to severe bleeding (hemorrhage) or dehydration Blood pressure less than 120/80 mm Hg is generally considered ideal. Levels higher than this increase your risk for cardiovascular disease. If you have unusually low blood pressure, have it evaluated. http://www.americanheart.org/presenter.jhtml?identifier=2152

Stress could be a major factor in high blood pressure.

stress and heart attack