My father has had three ablations and refuses to slow down, wonderfully. Plays one on one basketball with the neighborhood kids at 78. Hopefully you will stabilize and become better than you were before. Scary stuff though for sure.
The fact that your heart rate gradually came down would suggest that it isn't SVT. That starts and stops in one beat, one minute it's flying the next second it's normal. I would bet that it was simply a normal response to exercise, then you got scared, which caused it to go a bit faster. Maybe go a bit slower next time and as you gain confidence start pushing yourself a bit harder.