Currently I have no treatment. I tried Calcium & Beta blocker med's but stopped because of fatigue side effect. Then got evaluated for having an ablation and decided against it. I never had symptoms, so only knew from the Apple Watch and EKG. Also, the PSVT episodes essentially only happen when I run and stops when I break into a walk. (has happened, but rarely, during other exercises, like walking). I've run a 5K and 10K since diagnosed with no ill-effects. Cardiologist said PSVT is "rarely" fatal and let him know if I start having symptoms. As part of determining what I had, they ran a stress test, echogram and other tests which showed my heart is structurally sound. So only known heart issue is the PSVT.
As to why it started, no, I don't know. I had been running for about 10 years that included about 6 or 7 marathons. I noticed the tachycardia during a training ran half-way through a 3 month training program in prep for another marathon....and made an appointment with my doctor. Although the cardiologist didn't say I couldn't run ("rarely fatal"), I decided to stop as am afraid it could get worst. So now I do a lot of walking, which I enjoy.