Has he been too lethargic to eat or drink? How does his crop feel—empty and flat, full and hard, full and puffy? How old is he and what breed? Do you have any pictures of him?
Can you try to give him some fluids or electrolytes, even pedialyte or gatorade? If he is eating and drinking, and seems constipated, giving something like chilled coconut oil cut into small pieces for him to peck, or a little mineral oil in some cooked egg would be much safer.