Hello,
Firstly the numbness may be due to - repetitive-stress motion disorder . It can be caused by nerve compression. It may also be due to - circulatory,like poor blood circulation, neurological, or muscle-related condition.
If , it has occured suddenly then it could be a warning sign of an impending stroke.You need to exercise the hand muscles, you should avoid temperature extremeties, Also massage & relaxing therapy will relieve the stress & improve blood circulation.
You should see your Physician, to evaluate the condition and get clinical examination.
I hope this has helped.