What Causes Recurring Weak Spells?

My 85 year of father had a weak spell out shopping. Couple of days later his blood pressure was 222/95. Pulse on his blood pressure monitor at home showed 35. He spent a couple of day in the hospital, got his pressure down in the 160 s. Hospital didn t find any heart damage, They did perscribe Metropolo. My father has since had more of these weak spells. Any suggestions to the cause of this?