Take him to the vet. There are medications for canine anxiety.
Yes, dogs can have anxiety disorders and PTSD just like people.
The medication will more than likely be just to get him through the transition period.
Carry him outside if you have to, only stay a couple of minutes, bring him in and give him a treat. Just a small bite of something tasty, like chicken.
Same thing with the carpet offer him a bite to cross over.
Baby steps. Maybe a little more time outside every day. As he gets better make the treats smaller and smaller, like just a piece of kibble, as he will grow to expect something.
Don’t disregard the medication part, I’m talking about prescription meds via examination by a vet, not supplement waste of money crap.
Until you can reduce his anxiety (by meds and patience, tlc) he will be unable to relax and unable to learn anything, in fact he may get worse.
Good luck and give us an update. I was thinking of getting a greyhound myself, down the road, if I ever get another dog.
