Mr. Nelson is a 67-year-old retired insurance salesman with a 2-day history of dizziness. He describes a lightheaded sensation as though he is about to pass out that occurs whenever he is standing or walking. He has a milder sensation in the sitting position and is completely relieved when he lies down. There is no sense of spinning accompanying this sensation. What is the likely physiological mechanism underlying Mr. Nelson’s dizziness? Question 44 options: Depression or anxiety Diminished oxygenation of the cerebral cortex Stimulation of the vestibular system when he stands A cardiac dysrhythmia