I've brought fish home that don't make it. I can usually tell like you did, sitting on the bottom being inactive and being pushed by the current. I'm not sure there's much of anything you can do... Nothing I ever did worked!
Also, with Danios, they're schooling fish so they like to be in groups of 6 or more. I'm not sure what else you have in your tank, but they can be fin nippers. Even then, I had 6 of them in my tank and they nipped my cory's tail off. (Needless to say, I took them back to the store...) Just watch for nipping! I liked them, though. They were so funny!
Sorry about the fish!
