I get "vagus nerve episodes" as you are calling them from several causes:
I'm allergic/intolerant/sensitive to sulfites - which could have been sprayed on the clams as it is on shrimp and fish.
When my esophagus gets irritated I get spasms leading to palps and tachycardia - things like uncoated pills getting stuck.
When I was getting diverticulitis with an abscess my first reaction was 5 hours of tachycardia, then stomach wanted to vomit, finally, hours later I started getting the abdominal pain.
It's caused by esophagus, stomach, gut and heart being connected by the vagus nerve. It's called cardio-esophageal reflex (not reflux) or linked angina. If you google those words you will find medical research papers.