hopefully,
this was just 15 to 20 seconds of something "harmless" like SVT,
followed by an anxious or panicky reaction that made your heartrate skyrocket for 10 minutes or so.
i think the fact that the quivering lasted only 15 to 20 is actually reassuring,
but for total reassurance you would probably need a 30day monitor and if that didn't catch it - an electrophysiological heart study where they try to make your heart beat irregular and ablate it on the spot.
I dont know if it was irregular because during the quivering part I didnt think to check my pulse, and other than the pulsating odd feeling that went on 20 seconds, I felt fine, but during the fast part it felt steady, yet i near fainted. I did not eat anything new or get bit by a bug. I am certain this was not anything other than whatever my heart did. I had been having a lot of pvcs for aprox 7 months.
It's impossible to say - just as an example, I've asked a cardiologist on an internet service at least 10 times a similar question a while ago - and he ended up saying "you won't be happy until I say you did have VT" In other words: Not even a cardiologist can answer your question.
Quick VT causes hemodynamic instability - but so can SVT do, and people react different (depending on their hemodynamic reserves). Some people can faint during a 130 BPM VT or a 160 BPM sinus tachycardia. Other people can tolerate a 200 BPM VT without other symptoms than palpitations.
Anyway - the fact that your heart rate reduced gradually makes SVT/VT less likely. If it lasted this long (10 minutes or more), VT is less likely, if your heart is normal.
Afib causes grossly irregular heart rate. Was your heart rate irregular during the event?
If I should take a guess, I'd suggest hypoglucemia (low blood sugar), a sudden allergic reaction (did you eat something new? sting/bite by a bug?) or sudden adrenaline excess. Especially the two first suggestions can make you faint and cause a very weak pulse. Anyway, no one really knows, and it's important you contact your doctor immediately if you get similar symptoms.
As I said, If I should take a guess, I'd say this is not VT. But our guessing is a bit worthless here :(