Hi, I hope I'm not invading a thread about SVT, but I have a similar issue called Atrial Fibrillation. It is not the same as SVT but has many similar symptoms.
Believe me I totally empathise with you SVT sufferers. The feeling of total anxiety and fear that comes with a rapid heart rate or palpitations all over the place is something I live with too. It is bloody awful sometimes.
I've had cardioversion several times, but it didn't work so the heart rate had to be stabilised with other drugs such as Flecainide. Waiting for it to work has to be up there with the terror claustrophobic people feel in an enclosed space! Sometimes that doesn't work and a drug of last resort that actually stops and restarts the heart has to be used. You can feel yourself dying. Awful, but it usually works.
One big difference between SVT and Afib is that I had to take blood thinners to prevent stroke, but I don't think that's necessary with SVT. I was very lucky to be a candidate for a Watchman device that closes of the left atrium appendage (fascinating procedure, I could see it on the monitor, but was sedated and all relaxed and cuddly lol). So now I don't have to take blood thinners anymore, which is a great result. I still have Afib though and take beta blockers daily!
I also use the vagal manoevres, stick my head in a sink of cold water, do deep breathing and now and then take a low dose Xanax if I get very agitated. The manoevres often help, but surprisingly, if they don't a bit of vigorous exercise often does, such as walking up and down the stairs very quickly etc. But it's not for everyone.
Good luck on your journeys. I'll be watching the thread, and I hope I didn't butt in too much.