Firstly, I am glad nobody got shot. I noticed this was a scared myself thread, not a I just shot myself thread (which wouldn't have been posted most likely).
Second, I have never taken a safety course but I was raised with the following rules. They should be familiar.
1. Weapons are loaded until you have personally cleared them, always treat them as if they are loaded.
2. Always keep the muzzle in a safe direction, don't point it at something you wouldn't shoot.
3. Finger off the trigger until you plan to shoot.
4. Safeties aren't. All safeties can fail (I still don't see how on a hammer block, but I still count this as true).
How do those compare to the NRA safety rules? I hope you find out what happened and that you compensate / correct the condition that caused it.
Alan