My Brother Is Diabetic And Has Been Taking Rx's Prescribed

My brother is diabetic and has been taking rx's prescribed by his pcp at the va. This past week he caught the bug I had and was coughing like crazy and had pretty bad diahrreah so did not eat much. At the behest of his endocrinologist who advised that if he couldn't stay out of the bathroom he should not take the meds since they would not do him any good, he did not take anything but continued to monitor his a1c. He did take Robitussin DM Sugar Free for the cough and finished it last night. Needless to say his a1c was completely out of whack this morning. He has been dizzy today is now eating small meals. The sugar is coming down but still high and kinda yo-yoing ab bit. He has a call into his dr but they are closed until Monday. Are we doing correctly?