I have struggled with low blood pressure for most of my life. Sometimes nurses are shocked when they see what my blood pressure is. Basically, it means that your blood is not pumping at the rate it should. Most people worry about high blood pressure, which can cause heart attacks, but low blood pressure is dangerous too. It can make you weak. Since I am not a doctor, I sought out an article for you.
http://www.enotes.com/hypotension-reference/hypotension (low blood pressure)
Low Blood Pressure:
Blood pressure is the force created by circulating blood on the walls of blood vessels. Blood pressure is generated by the heart pumping blood into the arteries that modified by the response of the arteries to the flow of blood for the heart.
An person/ individual's blood pressure is expressed as systolic/diastolic blood pressure, for example, 120/80. Low blood pressure (hypo-tension) is pressure so low it causes symptoms of the low flow of blood through the arteries and veins. When the flow of blood is very low to deliver enough oxygen and nutrients to body parts such as the brain, heart, and kidney, the organs do not function normally and may be temporarily or permanently damaged.