I got the call just as he was being carted off in the ambulance, the first he's ever ridden in. This is only the second time in his life he's ever stayed in a hospital over night.
The bad news is that he's got pneumonia, and it's quite serious. The good news is, it's treatable. Given that he is essentially indestructible, I imagine this means that he will recover.
Whatever the case, it was very difficult to leave this evening, when visiting hours were over, and I'll be back tomorrow morning.
Too tired to write in depth right now.