Thank you for asking your query at DoctorSpring.
A normal blood pressure is a pressure of 120mmg or lower systolic and 80mmg or lower on diastolic. In some individuals it can go as low as 90mmHg/70mmHg. But this can be a 'low blood pressure'. Anything more than 129/89 denotes hypertension.
The blackout symptoms cannot be explained just by low BP. I would like to know some additional information about your symptoms, like what caused this ? (precipitating) factors. How many times this has happened ? Have you undergone and investigation (blood tests / MRI) ?
You can reply as a followup.