Review Question - QID 215174

A 32-year-old man is brought to the emergency department for evaluation after he fainted at work. He says that he was reaching up for a box stored on a high shelf when he felt lightheaded and fell to the floor. He says that this only occurs at work when he is looking up or turning around, and he thinks that it is due to him feeling claustrophobic in a dress shirt and tie. He has no significant past medical history and his only medication is occasional calcium carbonate for gastrointestinal upset. On presentation, his temperature is 98.6°F (37°C), blood pressure is 117/71 mmHg, pulse is 85/min, and respirations are 11/min. He says that he has no residual symptoms and is able to respond appropriately to all questions. Which of the following mechanisms is most likely responsible for this patient's presentation?