it seems there's actually tons of invincible frames in the dying state. just today I was surrounded by tons of zombies + a whopper, I can't tell if they attacked me or not, but I was moving around back and forth and no one hit me at all.
I thought only the beginning animation of the dying state have invincible frame, but it seems once you are able to control your character, you could move around in a certain fashion that MIGHT continuously supply you with semi-invincibility.
Toy Story 4 trailer, best movie 2015? https://www.youtube.com/watch?v=PGuTN_ilmEk