I found Gerry to be one of the most disturbing films I've seen in a while.
There's no zombie blood being spilled, but you get that same sick feeling in your stomach as if there was. As the character's situation worsens, and as they dig themselves into a deeper hole, you're left with little to do (intentionally) but ponder their situation and repeatedly ask yourself, "what the fuck are they doing? What the fuck are they gonna do?"
It's been a few months since I've seen the film, but whenever I see any type of barren landscape, be it a large, empty city park or a photo of the desert, that sinking feeling returns.