Andrea here, musing on “the Swoon,” one of the traditional minor but memorable secondary tropes of Regency romances. Fainting is far less prevalent in today’s historical novels—or it's used for tongue-in-cheek effect—as women aren’t as apt to be portrayed weak, flighty creatures. (What self-respecting modern heroine would fall into a faint at the first sign of trouble or bad news? These days, if accosted by a villain, she would likely punch him in the nose rather than swoon and hope to be rescued by her hero!)
But all jesting aside . . . the phenomenon of fainting from an emotional trigger (shocking news, fear, anxiety, etc) is actually a real medical condition called Vasovagal syncope. It happens when the part of the nervous system that controls heart rate and blood pressure reacts to stress. The heart slows, blood pressure suddenly drops, the blood vessels widen in your legs, causing the blood to drop to the lower extremities, thus oxygen has a hard time getting to the brain. So you, um, swoon. (It’s often called the Vagal Response because the vagus nerve is involved in controlling the blood vessels, and when it’s overstimulated by stress, unpleasant things can happen!)
How do I know this? Well . . .