[DISCLAIMER: I AM NOT SUICIDAL]
You ever wake up and go "Damn," because you realize you're still here and did not die in your sleep and thusly shall have to try to survive another day on this Godforsaken planet, only to go to bed hoping for better luck this time?
Seriously. I think the reason zombies shuffle aimlessly and eat the living is because they DIED. It was OVER. They could finally take their much deserved rest--only to wake up and realize that, first of all, they had to dig themselves out of their graves using only their hands, and secondly, they had to go back to this shit and the best they can hope for is that someone blows their goddamn head off with a shotgun.