Actually, this might be clinical.
People usually make an adjustment to their system so we can get up from a prone position to standing without passing out.
“When we stand up, the blood goes down from the chest to the distensible venous capacitance system below the diaphragm. This fluid shift produces a decrease in venous return, ventricular filling, cardiac output, and blood pressure.
“This gravity-induced drop in blood pressure, detected by arterial baroreceptors in the aortic arch and carotid sinus, triggers a compensatory reflex tachycardia and vasoconstriction that restores normotension in the upright position. This compensatory mechanism is termed a baroreflex; it is mediated by afferent and efferent autonomic peripheral nerves and is integrated in autonomic centers in the brainstem.”
“Drug therapy alone is never adequate. This condition has no cure, symptoms vary in different circumstances, treatment is nonspecific, and aggressive treatment can lead to marked supine hypertension.”
That is, when they stand up, their blood pressure drops so much that they feel faint, but if given drugs to increase their blood pressure, when they lay down, they get high blood pressure.
A possible mitigation for this effect may be for the “patient” to do a few leg isometrics before attempting to stand. The muscle squeezing forces blood from the lower limbs to the heart where it can be routed to a useful location in the body (head).