Anything that causes you symptoms - though 80s/50s(or lower) is considered too low. A reading like 105/75 would still be in the normal range and readings like 90s/60s would not be considered "very low" (despite what most who post in that range think :rolleyes:) it would still be considered in the lower end of normal.

This is in the absence of a person normally having high blood pressure and/or using medications to lower it.