I have cystic fibrosis and often cough quite vigorously. This morning I believe I strained my back while coughing. I was coughing a felt a pop of sorts and then sharp pain, which has eased throughout the day. I use a vest machine for airway clearance twice a day, which shakes my upper body around my lungs to loosen mucus. Is it safe to use this with an injured back or should I seek alternative forms of airway clearance?