You are considered to have hypertension if your systolic blood pressure measurements are between 130 and 139 or your diastolic measurement falls between 80 and 89. At this level of blood pressure you may not have any symptoms. When blood pressure reaches 180/120 or higher, a serious condition known as a malignant hypertension or hypertension crisis may occur. This can lead to stroke, kidney damage, heart attacks, or loss of consciousness. If you measure your blood pressure and it is this high, rest a few minutes and measure again. If it remains high, call 911.
Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure symptoms tend to be more upfront and easily recognizable. The development of symptoms is often a warning sign of a potentially serious underlying disorder. Generally speaking, your blood pressure would need to fall pretty dramatically before symptoms develop.