... after my wife tried to remove one of those discount tags from my key chain. I thought I'd killed it when everything went off (dash lights, radio, etc.)

, but then realized she must have done it while messing with the key chain. Fortunately, we were able to pull over and sort it out. The key looked like it was still in the on position, but she must have bumped it or it's extremely sensitive. We had a good laugh after figuring it out. After turning the car off, removing the keys (and the offending discount tag), putting the keys back in, the car started up and ran normally.
So, don't try this at home and don't mess with the key chain (even if being very careful) while the car is zinging down the interstate.