He might have got a cold. Make sure that you cover his frail body with something warm. Give him warm milk to drink and consult him to your vet so that he can give medications for the cat's speedy recovery.

Hurry!

 Your cat may have an upper respiratory infection which would account for the sneezing. I had a cat with this very scary problem one time and he also was drooling which came from an ulcer on his tongue. Biostudent is right, you need to get your cat to a vet. These infections require care and can become life threatening.