First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes. The heart has connections to the autonomic nervous system that helps control the rate of the heart beats. The sympathetic nervous system speeds up the heart and the parasympathetic (through the vagus nerve) slows down the heart. These are important controls and are supposed to balance each other. Sometimes discharges from the brain (for unknown reasons)can cause over activity of one or the other. When the heart slows down, this can cause a person to pass out (vaso-vagal syncope). When this happens it is often self limited and rarely causes any permanent damage (because the heart speeds back up itself, called the vagal-escape). However, sometimes heart problems can present with the same symptoms as vagal type slowing, such as heart attacks and/or heart electrial problems. I would recommend a heart disease workup including thalium stress echo to examine for reversible ichemia and a heart vessel angiogram. I would also recommend a tilt-table test to examine the effects of your vagus nerve on your heart. After these tests (if normal), it is likely you will be able complete your surgery with out further incidents. I do not think your chiropractic manipulation had anything to do with the response of your vagus nerve. I hope this has been helpful.
The answer is yes, but it is unlikely that vagus stimulation would have an effect several hours later. The vagus nerve is close to the carotids and also down by the anus, and when stimulated the heart rate drops. Normally there are several back-up pacemaker sites and the heart rate will not drop below the level necessary to sustain life. If, however, there are existing cardiac irregulities, vagal stimulation can induce what is known as R on T phenomena. To make a long story shortn the heart goes into ventricular fibrilation. This is why many people are found dead on the toilet. The heart rate drop after vagal stimulation is rapid, however, and the heart rate returns to normal after the stimulation is stopped.