I guess when you do a walk-through of the apartment, checking that the doors and all windows are locked, four times before you finally concede that yes, it is safe, and no, serial killers won't break in and/or zombies are not going to jimmy their way in and gnaw on your feet in the middle of the night...well.
And yes, thoughts like that do actually go through my head. I didn't worry about zombies eating my feet until I watched "The Walking Dead," though. It's just...so wrong. On eighteen different levels.
I'm going to go check the sliding glass door again. Just once more.