Thanks so much, dizzyizzy - that's incredibly helpful! Just to make sure I know what you're saying (and to try to put it into an image) - basically, SVT is like a square wave where you go up from normal to high immediately and then down back to normal from high at some point later, again immediately? And POTS/dysautonomia arrhythmia is more like a sine wave - it goes up and down with a slope rather than immediately? If I'm understanding that right, then what I seem to have all the time is POTS-type stuff. If it weren't for the weird p-wave morphology, I wouldn't even suspect an SVT (in my case the atrial tach) at all. I don't get random jumps in heart rate - or at least, if I do, they're not symptomatic. So I could have had that my whole life and not noticed, maybe, and noticing the development of POTS is what led to the diagnosis of the atrial tachycardia as well? What you describe as sudden, unprovoked rapid heart rate is something I've never felt; I always have that slow build-up, and it's almost always after doing something like standing up or doing exercise. And yeah, afterwards I'm always wiped, but it's easy to stop it by just sitting/lying down; it never just fails to stop. Thanks for the extra info on the ablation. Will definitely skip that. In my case (with atrial tachycardia) the doctor said that they wouldn't necessarily be able to find the extra pacemaker cells to ablate if they couldn't trigger the abnormal p-wave morphology, so it might not even work, which made me even more hesitant to consider it. I'm glad that I had read stuff on dinet before so I knew to refuse initially! re: medication - the electrophysiologist said that we're trying calcium channel blockers because of my mood episodes - apparently beta blockers can trigger/worsen depression - but that if those don't work we can switch to an anti-arrythmia drug. But I hear those come with a very low (but it's there) risk of sudden cardiac arrythmia/death, and I'm not so keen on that. So far the calcium channel blocker doesn't seem to do anything for the dysautonomia stuff other than perhaps slowing the tachycardia a little bit. My resting heart rate is usually around 60 (although the Holter got down to the upper 40s overnight), so they weren't worried about that.