What attacked him? Be sure to look him over THOROUGHLY for injury and treat accordingly. Be aware that shock can kill birds too, even if the predator didn't injure him.
If you find no injuries, put him in a quiet place with no interruptions with food and water so that he can recover. Give electrolytes like Gatorade (we use Sav-A-Chick brand Electrolyte packets that can be found at feed stores because they're easy).
Make sure he's comfortable and is not subject to loud noises like doors slamming, kids yelling, pots banging on countertops, etc. Observe him over the next few days and visit him occasionally, talking softly to him, reassuring him that he's okay and that things will be alright.
It just takes time...