Just an update: this morning they called an ambulance to take him to the hospital. Due to his upper body weakness, which has gotten worse, they now suspect a stroke or blod clot, so they’re scanning him up one side and down the other. The good news is he’s on a morphine drip now, and there are qualified people taking care of him; good for him, good for my mom, to be bearing less of the burden. Hopefully it doesn’t turn out to be something too awful. His brain seems to be working in its normal, analytical, cranky way, so that is good.
Thanks for the update. I’m glad to hear he’s getting help. And cranky is good. When cranky patients turn docile and agreeable, I get worried. 
Final diagnosis: polymyalgia rheumatica.
So no strokes or anything life threatening. They put him on prednisone and he is now able to get up out of bed and make his way across the room without assistance. He may be discharged today, and they are making plans for medical equipment, home health care, therapy, and continued appointments with a rheumatologist. So hurray for the hospital!
Thanks again everyone for all your ideas and support!
Make sure he keeps up those appointments. This is one of those conditions which responds quickly to initial treatment, but requires 2-6 *years *of low dose medications before it resolves completely. People tend to feel better and then get fed up with the maintenance and stop seeing their rheumatologist, and then it comes back worse. Also, watch for Depression - no one knows the reason (whether it’s just because pain sucks, or a side effect of the meds, or if there’s a neurotransmitter glitch or what), but Depression often develops in patients with polymyalgia rheumatica. Yet doctors rarely remember to tell people that. (Maybe they don’t want to plant ideas? I don’t know.)
But all in all, good news! There are many worse things it could have been, and while pr is no picnic, it’s pretty manageable. 