Flattening of the diaphragms bilaterally, on chest X-ray, is usually associated with over-inflation of the lungs, COPD and asthma being the most causes of such flattening. It is extremely unlikely to be related to your dog jumping on your chest. Further testing, to include pulmonary function tests, would be appropriate at this time. You should also ask your doctor his/her opinion of what has caused the “flattening.”
Good luck
ive already had the lung tests. they are not good