Young sparrow breathing hard

I found this young fellow on the side of a street, checked for its parents, but no one around - except cats and crows who seemed to be interested. So I picked it up. It was breathing hard and offered no resistance. I took it home. I gave it some porridge and crushed bird food with water, and it got lively for a minute or two. Since then it seems to be sleeping, but it continues to breathe hard. I don't want to disturb it when it sleeps, but I am not sure if it needs more food. Will it tell me? Does it have a chance.