So, in other words, low blood pressure may be caused by both low cardiac
output ( for example dehydration or heart
failure) and low resistance (dilated blood vessels due to heat, autonomic failure, BP medication overdosage, etc..)
Usually, the heart rate increases with low bp, to increase cardiac output. If your heart rate is 67, the body thinks the BP is okay. That's a bit unusual if you are having symptoms, but really common with beta blockers, like Woogie said.