I don't have the numbness, but I sometimes get cervical migraines.
There are simple stretch exercises you can do several times a day to keep your dystonic neck muscles in shape. In my case it helped a lot to change pillows, my back hurts much less since I sleep on a Tempur pillow, which keeps my neck and back properly stretched while sleeping.

Also, and this is very important, keep your neck muscles warm, i.e. wear a scarf if you live in a cold climate, or polo shirts if you live in a warm one with air conditioning everywhere.

Take care
Teresa