Welcome to the forum, Marcea.
My major reaction to sulfites is tachycardia too, also usually not a very high rate or lasting more than an hour or so. I've been to the ER often enough, once had to have chemical cardioversion because I'd tried everything else and couldn't get the rate below 145 - 165 after 6 hours.
Yes, the usual tests will come back normal. The vagus nerve is indeed involved, because the intolerance starts in the esophagus and stomach, which are on the vagus, and then that triggers the heart. I once had a heart attack caused by the vagus stimulating the coronary arteries to spasm, blocking the artery 95%.
This condition is known as linked angina or cardio-esophageal reflex. There are more papers on the subject all the time.
You may notice a feeling of a gas bubble just before a little gastric reflux or jumping feeling in the stomach just before the tachycardia happens. Or the tach may take hours to develop. I sneeked a small glass of wine this evening with dinner, and 3 1/2 hours later have a little tach going on. I take Inderal right away when this happers - prescribed by my cardiologist. It doesn't work long, but the tach doesn't usually last long either. It does act very quickly, which I appreciate, since another heart attack could happen quickly too.
KEEP A FOOD JOURNAL! Every day for a few months at least, write down everything you eat, drink, all medicines, the time and any reactions. When you note a reaction you can look up the page and find out what you might have eaten that triggered it. Write down little things like the feeling of a gas bubble, stuff you'd ordinarily ignore.
My heart attack was precipitated by eating a bowl of cereal with some lovely dried fruit for breakfast.
Look up how to do Valsalva maneuvers - of course, check with your doctor! I find it often stops the tachycardia if I push hard like going to the bathroom or getting up a gas bubble.
If you think you are having a heart attack chew up an aspirin and call for transport to an ER.
It's not necessary to avoid ALL sulfite. A lot of foods have it in small doses that won't bother most people with the sensitivity. It's easy to avoid processed foods, especially the ones with too many ingredients. I nearly went to the ER after foolishly eating a store-cooked chicken pot pie. They didn't make the pie, just cooked a frozen one. Grocery stores don't make their own bread dough here (US) either. A couple of slices of toast will set me off unless it's "preservative free." Keep reading the old threads. There's lots more information.
Interestingly, the lower gut, which is also on the vagus, can trigger tachycardia. I've had that happen when I was had a ruptured diverticulum. If you have diverticulitis, you might want to consider this as a pssibility for a cause, if finding trigger foods doesn't work out.