I had my first major heart palpitation over 10 years ago (190+ bpm) and gave up the cigs due to it. But since I have had many more some as big and some as not.
About 6/8 weeks ago I vomited with triggered a bad A-Fib (irregular heartbeart), I didn't panic whatsoever due to experience if you panic your basically fucked. This one A-fib even standing up to go for a piss my ECG was hitting 260+ BPM probably even higher I dont know but I was calm and relaxed but Jesus if you panic on that high heart rate you would be dead. I spent nearly 3 days in hospital until it back to normal . I got a random one out of nowhere a few weeks ago, irregular heart rhythm but not high heart rate( I said I am not spending the night in hospital) it passed eventually after 12 hours thank god. They want to see me every few weeks now ffs
Anyway short story short, never panic when your heart is acting funny, sounds stupid but if you panic it makes things 20x worse. I've been calm even when hitting 260bpm+, your mouth will dry up quick if you hit those levels that's it.
And also I wouldn't wish it on anyone