Hi Capin ,
don't be alarmed that your medical status changed to Not needed at this time , and I guarantee to you it doesn't mean ( it means "Not needed at this time means we have not yet received an application for permanent residence. You need an invitation to apply before you can submit an application for permanent residence." ) that's a general explanation that CIC had put there and it's not specific to your exact case .
Chances are your medical has expired , CIC didn't extend it and they don't need new ones at this time , they will inform you in writing if one is needed when time comes .
You can use your MP help to check on the status of your medicals .