Final answer:
Post-mastectomy numbness is common, caused by nerve trauma during surgery, and typically dissipates over months, usually resolving after about a year, although some permanent change is possible.
Step-by-step explanation:
The numbness in the area of the surgery and along the inner side of the arm that the client is experiencing post-mastectomy is not uncommon. It is due to the trauma and inflammation to the nerves in the area during the surgical procedure. While this sensation can be concerning, it is generally not a sign of a complication. In most cases, such numbness will dissipate over several months and usually resolve after about a year as the nerves recover. However, some degree of permanent change is possible depending on the extent of the surgery and individual healing processes.