This was not an over-the-wing door, as I was just one row away. It was definitely way back in the aircraft. I suspect the person in question was going to the loo, as you UK types call it.
To answer cwatters: I should have led the crowd in a rousing version of "You've got trouble, right here in RiverCity, with a capital T and that rhymes with P and that stands for Pressurized Plane Plummeting."