I had cardioversion once and it was not a pleasant experience. I went to the ER with an Afib episode, and they could not get me back to NSR. After about 2 hours they asked me if I wanted to have them try cardioversion., otherwise they would discharge me with some additional meds. I opted for the cardioversion. I was told I would receive 2 IV drugs, one to sedate me and another that would block any memory of the procedure. They gave me the sedative first, and I must admit it made me feel pretty jolly. Then I got the anti-memory drug. But guess what, I was still very much awake when they zapped me! It felt like I got whacked on the head with a 2x4, only worse. I looked at the docs and said what the hell was that! They just looked puzzled and sheepishly said, um, I guess next time we need to give you more sedative? Anyway it worked, instantly. I converted back to NSR. Had another Afib episode about 5 weeks later.