When tested with a "blood pressure monitor", low blood pressure is that below 10> 6, or 9> 6. Low blood pressure can be a physical condition, but it can also be a sign of disease. There are reasons for low blood pressure such as: small dilated blood vessels, heart problems, excessive water loss, dehydration, blood loss, kidney disease, stress, fatigue, can also be allergic to certain medications. Signs: Dizziness, fatigue, heart palpitations.