Archie, is it possible someone's been using pesticides or other chemicals in an area where the kitty could have inhaled a lot of it, or gottten it on his skin? My sister once had a cat that she washed in flea soap intended for dogs, and the poor kitty had such awful after effects--staring into space, would not eat or drink, and didn't even seem to notice the food and water. She did seem to watch things that no one else saw, and it was very weird. The vet said to wait a few days, and it might improve, but unfortunately Mitty got worse, growling at 'nothing', falling down and so forth, so she had to be put to sleep.
This was years ago, so maybe if your cat has contacted poison the vet might have better treatment for it?