But if your blood pressure drops suddenly or causes symptoms like dizziness or fainting, it is too low. It can cause shock. Shock can be dangerous if it is not treated right away. Blood pressure is a measure of how hard the blood pushes against the walls of your arteries as it moves through your body.omeone with a systolic pressure of 120 and a diastolic pressure of 80 has a blood pressure of 120/80, or 120 over 80.. Normal blood pressure is lower than 120/80. Low blood pressure does not have a specific number where it is too low.