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Low blood pressure is hard to define, because a lowered blood pressure can occur naturally in persons who exercise regularly, keep a normal weight, and eat a healthy diet. Many experts use the arbitrary criteria of a systolic (top) pressure of 90 or lower or a diastolic (bottom) pressure of 60 or less to be the cutoff levels used to define low blood pressure. But in some cases, low blood pressure accompanies certain medical conditions and may be a sign of life-threatening illness.
Low blood pressure may be a sign of multiple conditions, including dehydration, severe infection with septic shock, endocrine (hormonal) conditions, some heart diseases, and taking certain medications. Psychological stress is not a known cause of abnormally low blood pressure.
U.S. National Library of Medicine