I thought I would show a graph representing arterial pressure (systolic and diastolic) over a twenty four hour period for one individual.

What is Health? 2020

What it shows is many peaks and valleys of blood pressure. So, when they ask: what is your blood pressure? it varies all over the place according to what’s going on in your mind.  So, for example, at one point it is 3 in the afternoon and the individual is dozing during a class lecture and the blood pressure comes down. At this point, a neighbor sticks him with a pin. His brain predicts danger, and the pressure shoots up rapidly. He looks around and realizes that this is a prank, and his blood pressure comes down. At midnight, he becomes sexually aroused and his brain predicts the needs for a higher level of blood pressure. And afterwards, the brain predicts that a lower pressure is needed that allows for sleep. And the next day he is coping with challenging conditions and the blood pressure is back up to a pretty high level.