I agree, you need some GFI installed. I would have gone for the power strip to flip the button, had a friend or two get shocked when things like heaters bust open. No matter how many probes you put in your tank if that much power was sitting there it's not going to take just one path. Any kind of ground will have more or less juice flow depending how well it's grounded (maybe enough to drain the lethal limit). I doubt you can put enough probes to stop it. If your concerned about your fish they won't feel anythin *needs a pro to confirm that bit of info* From my experience, one of my friends marine tanks had a fault somewhere in the electrical that would give him the shock of his life, he didn't find it till a month later in a rio pump I think, either way the fish were fine. If something like a light is in your tank don't ever put your hand in there till you cut the power by pulling the plug or switching off the power strip. I'm no doctor but I'm guessing a shock like that could have stopped your heart. We all learn lots by doing so next time I'm sure you won't be so quick to stick your hand in the tank.
If your arm still feels funny you might want to see a doctor.