Hope he gets feeling better, my wife and I both and pneumonia about 5 years ago at the same time, if someone hadn't taken our two kids for 3 days who knows what would have happened. Lots of rest and medicine make a big difference.
The thing that made the difference for me was hiking. Its more exercise than walking, doesn't kill your legs like running and its a good workout. Plus it has a low barrier skill entry, if you can walk you can hike. :)