Symptoms of high blood pressure (hypertension) usually do not develop over days, weeks, or months. It often takes years for symptoms of high blood pressure to become noticeable. People who exhibit symptoms of high blood pressure may experience nausea, dizziness, headache, and blurred vision. About 1 percent of people with hypertension do not seek medical care until their symptoms become severe. In fact, high blood pressure is commonly referred to as "the silent killer" because its symptoms are often mild and nonspecific (meaning they could be caused by several different conditions). Severe high blood pressure is referred to as malignant hypertension, and it occurs when the diastolic blood pressure (the lower number of a blood pressure reading) often exceeds 140 mmHg. A person with high blood pressure this severe requires immediate hospitalization and lowering of blood pressure to prevent brain bleeding or stroke. A few of the symptoms of severe high blood pressure include headache, nausea, and lightheadedness.