Update!
Cairo is doing great! He is completely back to normal.
I fed him a newborn pinky rat last Wednesday, which he took with great enthusiasm! He defecated normally a few days later. When I checked in on him last night, he gripped me tightly with his back end! No weakness or difficulty moving through my fingers!
I am quite relieved! I wish I knew what it was, but I am so glad to see him back to his normal self.