"Calm down" is a phrase that we all use, especially with kids when experiencing intense emotions. Here are some alternative phrases that just might yield better results, and an action plan to put them in place.
Being aware of these things could greatly increase doctor-patient relationship. If a doctor is more personable, the patient will be more willing to listen to them. If the doctor has higher expectations of the patient (either in the procedure being done or recovery time) the patient will do better and try to meet those expectations. It's simple psychology, really.