Doctors do not have a set number to indicate low blood pressure, according to WebMD. Blood pressure is too low when it causes symptoms or drops suddenly. Low blood pressure symptoms occur at different readings for different people, but they happen most often when pressure drops below 90/60.
Low blood pressure is called hypotension. Low blood pressure can occur if a person gets up too quickly, stands for long periods of time, is dehydrated, or suffers a trauma with severe pain or bleeding, according to WebMD. People taking blood pressure-reducing medications can also experience low blood pressure. Symptoms of low blood pressure include dizziness, fainting and shock.