The doctor. most likely, is referring to the settling process. In this process, the muscles are still adjusting or on the process of healing so he is experiencing some back pains due to this. Once the muscles are settled in place, he would feel normal again.
This, the least common type of ADHD, is characterized by impulsive and hyperactive behaviors without inattention and distractibility. ADHD, inattentive and distractible type. This type of ADHD is characterized predominately by inattention and distractibility without hyperactivity.