I have an 11 yr old chihuahua mix, part Pom/hairless chihuahua. For 5 yrs he has been on heart meds for murmur and lasix. Had him to the vet a month ago for rabies and boosters; he was also coughing a lot. Tried allergy meds and cough meds...no change. Vet xrayed for collapsed trachea. Heart looked good and no collapse. Now he has started stumbling, falling, can't get up. He still eats and urinates and has normal bowel movements. He screams just out of the blue, even when he is laying down. So he is coughing, screaming and stumbling...any ideas?