The Vagus Nerve is one of the twelve paired cranial nerves--it starts in the brain and travels through your neck, thorax and abdomen. The nerve "touches," or innervates, different muscles and organs as it travels down your body. One of its many functions in the body is to "slow things down" (this is called parasympathetic innervation [PI]).
Parasympathetic innervation is commonly referred to as anything that enables the body to "rest and digest." Thus, PI is involved in digestion, etc.
Another type of innervation is sympathetic innervation, which is commonly referred to as "fight or flight." Meaning this type of response is activated during activities like being chased by a bear--it increases heart rate, dialates bronchial passages in your lungs, etc. It can be thought of as the opposite of PI innervation, so digestion will be put on hold.
It is interesting that your doctor called this "vagus nerve response," as the vagus nerve is key in slowing heart rate (consequently lowering blood pressure).
From my uneducated perspective, it sounds like your blood pressure increased due to sympathetic innervation----your body was experiencing pain and was gearing up to "fight or flight."
I hope this makes sense and isn't too detailed.
Justin
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