I was assured that no one went into my room... that they knew of... key words there.

The reason I believe his back to be broken is just that he appears paralyzed from a certain distinct point in his body, down the rest of the way. Almost as if, two thirds of him is already dead. I had fed him right before I left town, so maybe just the extreme heat caused a gaseous eruption in his stomach as the prey broke down, which would have the effects of causing infection and bloating in the general vicinity of the rupture as he went septic, and swelling putting pressure on the spinal nerve causing him to be paralyzed from said point down. Problem is, neither of these options really provide any light at the end of the tunnel.