Hypertension usually takes several years before developing any noticeable symptoms, and even then they are often mild and nonspecific (meaning they could be caused by several different conditions). As a result, hypertension is often referred to as "the silent killer." People with hypertension typically don't even realize they have it until they have blood pressure readings that are too high.
When symptoms do occur, they can include dizziness, blurred vision, nausea and headache. However, many people don't seek medical care until they have more severe symptoms from the organ damage that chronic hypertension can cause.

Hypertensive crisis is a state in which blood pressure becomes so high that it is causing immediate danger and needs to be reduced rapidly. A person is said to be in a hypertensive crisis when his or her blood pressure is severely elevated and there are signs or symptoms of damage to the brain, heart, kidneys, or other organs.
Typically, a person in hypertensive crisis has a diastolic blood pressure (the lower number in a blood pressure reading) greater than 120 millimeters of mercury (mm Hg). In comparison, normal diastolic pressure for an adult is less than 79 mm Hg. Diastolic pressure refers to the pressure of blood in the artery when the heart relaxes between beats. Quick-acting medications can be used to reduce blood pressure during hypertensive crisis.

Over time untreated high blood pressure can damage organs such as the heart, kidneys or eyes. This may lead to angina, heart attack, heart failure, stroke, kidney failure, peripheral arterial disease, and retinopathy.