Should One Continue Taking Prescribed BP Medication If Their Blood Pressure Occasionally Drops?

Hi Sir/ Madam, My father is having high BP in sometimes. At times it fluctuates, it goes up and below the normal level. At that time he feels uncomfortable and guidiness. So we consulted a cardiologist and he prescribed Am long 5 mg morning and night. Actually he is a low bp gastric patient. For the past three years he started having high bp due to insomnia and having psychiatric medications. My question is if his bp is low for two or three days is it necessary to take bp medicine or reduce the dosage? Kindly advice me sir/madam