A sudden behavior change is a reason to see the vet. A dog may become irritable if he is in pain. Your vet will be able to insure the dog is not sick or injured.
If you have changed something suddenly then it is affecting the dogs temperament. For instance food, excersise schedule or playtime or maybe you arnet paying it attention.
I would take the dog to therapy. They have therapy for dogs. You may have to do a little research to find a doggie therapist in your area. Otherwise you can see if you can pinpoint why the dog's behavior changed.
