FIRST AND FOREMOST, YOU MUST GET YOUR BIRD IN TO SEE AN AVIAN VET IN YOUR DRIVING ARE. This should have been done immediately, and now it is critical that you take him in.
What happens with cats as they may just scratch the bird a bit, and this will cause an infection that kills them. Cat scratches and bites are deadly for birds, and only a little scratch is enough to start a full-blown infection, so please do not delay taking him to the Avian vet as your time may be very limited.
And yes, birds can be traumatized, and I believe this is MORE than that, so make appointment, bundle him up good so he does not get cold and get him in there quickly as you may wish you did later. For trauma, it will just take time and lots of love and patience. Put yourself in his place with a huge monster with teeth and claws after you, and you'll begin to get the idea here.
Lots of people do not understand what a cat attacking a bird means. It sometimes means the bird dies from a horrible infection caused from cat teeth and/or claws. It is not something to take lightly.For anyone reading this who has a cat or cats, always be nearby when your bird is out of cage as this happens when you least expect it, and is deadly for birds.
Let us know what vet has to say, and hope all is well.
