The thing that's surprising to me with so many performers seemingly walking right off into la-la land is that OSHA and the entity that oversees specifically stage riggers (they take this stuff very seriously! Becoming a certified rigger damn near requires an engineering degree - seriously!) has very strict and concise guidelines regarding every aspect of the stage with the edges, pits, and perimeters having some of the most technical and rigid rules. For instance, these areas not only have to be illuminated by reflective tape/paint within so many feet of them, the level of illumination itself is specified and must meet its own set of guidelines. Yet, for some reason, these accidents are happening more frequently.
Like Don said above, Arnel's stroll into the abyss was an outright header. He clearly had no clue he was even close to an edge. Those kinds of falls where you don't even realize you're falling until you're actually ..... well, falling can be the worst.
Think about a time when you've run into the dishwasher door when it was down. In most cases, you probably realized it was down at some point during your stride and even though you made contact with it, you were able to at least make some adjustment in how hard you actually connected with it.
Now, think about those times when you connected with it full-stride, completely oblivious to its presence and proximity to your shin! Even if you don't end up actually falling down, that particular pain experienced by a blast to the shin is a special kind of hurt all its own!
Poor guy.... bruised bones, bruised muscles and definitely bruised ego. Hope he's alright.