You never had a panic attack. When the brain overloads in such situation will take the most extreme action it can, shut you down, put you to sleep so you can't feel anything probably. It won't happen to everyone but it does to many. I've had some panic attacks 5 years ago that got me close to that point. I didn't pass out but I was right there, in all instances I ended up in the ER though.

I have a friend who's girlfriend was driving one day and the car slipped off the road going towards an electrical pillar (it didn't hit it though because my friend managed to grab the wheel). Near the collision point with that pillar his girlfriend passed out, in an instant. We laughed at that situation for years. They ended up in someone's yard, killing a poor dog in his little house.