What a terrible situation! Don't want to scare you, but it sounds like he's been exposed to something toxic. It reminds me of a big scheme involving the massive sale of toxic rape-seed oil here in Spain back in the 80's, (it was found to have motor oil in it) and which left hundreds of people with paralysis and/or Parkinsonism.
I hope it's just temporary and that he recovers completely. It could be so many different things, though, from pesticide exposure to a brain lesion (has a vascular accident been ruled out?).

Hang in there and tell him to be patient until the docs know what it is and keep us posted.

Take care
Teresa