That's okay. When I fast my blood pressure hits rock bottom too. It also takes me a week to recover. I have a BP monitor too. I won't attempt another fast until I can get my BP up to at least 110/70. When I fast my heart beat goes really slow and weak that I can't even feel like there's any heart beat at all. That's why I am envious of people who can fast past 4 days.
Low blood pressure can be an indication of low calcium. I know that blood serum levels of calcium remain constant, even when low in calcium because the body automatically leaches it from the bones. I think my bad reaction to fasting is a lack of essential minerals. Maybe you could try taking a good chelated calcium and magnesium supplement, making sure to take vitamin D with it for absorption.