I dont know about the breathing hard. But, If your dog has hookworms you can treat it with Panacur, Its always worked well for us. I had a dog that was loosing lots of weight and looking real tired and weak...but he was still eating. He had mucus with a little bit of blood in his stool, so we took him to the vet and It turned out to be hookworms. He was so aneamic that he had to have a blood transfusion. If it is Hookworms make sure to start treating your dog because it can get worse. Also, because our dog was still wanting to eat, it helped keep him alive so if your dog is not eating I would really be careful and watch him while your treating him.
I hope your dog gets better.
Keep us posted
-Cristina
