Hypotension, or low blood pressure, can cause numerous health problems, some of which are life threatening.
Simply put, blood pressure is a measure of how much force your blood places on artery walls every time your heart beats. Blood pressure readings measure two separate events: systolic pressure or amount of pressure that occurs when the heart beats, and diastolic pressure or the amount of pressure that happens when your heart is at rest between beats.
The two measurements are expressed together and provide an indication of whether or not there is normal or too much pressure placed on the artery walls when the heart beats. The following blood pressure ranges are generally accepted:
• Hypertension or high blood pressure: 140/90 or higher
• Prehypertension: between 120/80 and 139/89
• Normal blood pressure: 120/80 or lower
• Hypotension or low blood pressure: 90/60 or lower
Because pressure exerted is lower than normal with hypotension, vital organs get insufficient blood.
https://www.empowher.com/low-blood-pressure/content/hypotension-or-low-blood-pressure-when-low-isn-t-good