Blood pressure: How low can you go? What’s considered low blood pressure for you may be normal for someone else. Most doctors consider chronically low blood pressure too low only if it causes noticeable symptoms.
Some experts define low blood pressure as readings lower than 90 mm Hg systolic or 60 mm Hg diastolic — you need to have only one number in the low range for your blood pressure to be considered lower than normal. In other words, if your systolic pressure is a perfect 115, but your diastolic pressure is 50, you’re considered to have lower than normal pressure.
A sudden fall in blood pressure also can be dangerous. A change of just 20 mm Hg — a drop from 110 systolic to 90 mm Hg systolic, for example — can cause dizziness and fainting when the brain fails to receive an adequate supply of blood.