My eldest son suffers from this and has been hospitalised twice. The first time he was given medication to stop it, and a follow up appointment with a cardio specialist and had to wear a monitor for 24 hours. Nothing showed up and that was that. Second time, a number of years later,he was away from home and took himself to hospital where they monitored him for a while and it stopped spontaneously.
I'm not quite sure how often it happens now as he lives away from home and doesnt mention it, although i know hes not been hospitalised with it since. He was given a technique, a bit like bearing down, to stop it in its tracks when he feels it coming on which does work. He was told that if it didn't work then to not wait longer than half an hour before getting help.