Everyone has a differant range of BP's that "work" for them. If I was at 90/59, I would feel effects like yours. 10 points lower, I would faint. Blood pressure is compiled by the average of your b/p's, but if you find yourself dipping too low, you should ask your doctor. Sometimes a snack on something salty can bring you up a little, but this is a short term fix.
90/50 is considered low b/p. Drinking 16 oz of any kind of fluid in a 15min period will bring one's b/p up for two hrs. I've had to do this before when my b/p dipped too low. Drink enough fluid throughout the day so that your urine is a light yellow color. Start using the salt shaker. Fam
First, why did your b/p fall? Was it through another illness or medication? Mine is usually normal but I am epileptic and when I have fits my bp falls very low, in the region of 90/55To try to bring it back to normal, I increase salt and drink plenty of liquid, any liquid not just water. My husband suffers with extremely high bp so I just do the opposite of anything he does that usually works.