I had tachycardia starting at 17, on and off. Later in life, I switched over to the atrial fibrillation which NurseNancy has. Mine is paroxysmal, that is, I don't have it all the time.
I agree that it can be triggered by food additives. I am much more likely to get it if I have
had food additives, which means I don't eat out in many places. Also I am more likely to get it if I eat a meal heavy in fat (like red meat) which I'm not supposed to do on the Swank diet anyway. A-fib is different than tachycardia, and I recognized the difference right away, but when I had my first attack about six years ago I just felt exhausted and could not tell what was going on. I checked my heart rate and it was very fast and weak, so I called 911. I take l5 mg a day of Propanalol, a Beta blocker, in 5 mg increments (with each meal, or take at bedtime if I forget the one at dinner time). I am in danger of clots from Polycythemia Vera, too. I believe following the Swank diet and
curtailing excess salt has kept me so far from clots, but I probably do have tiny clots in my toes, where the thick blood from PV may clog my microvascular system and irritate the nerves, thus increasing neuropathy to the acute pain level sometimes.

Once I got Tachycardia from a big dose of Vitamin C--probably with an additive, as it came from a health food store which I learned later has products with a lot of additives.
I read labels.