What causes sudden loss of muscle control in hands?

May be neurological: Loss of muscle control can be due to problems in the brain or the nerves that control the particular muscles. A primary care doctor and a neurologist can evaluate to see where the problem is (the brain, the spinal cord, the nerves in the arms/hands, the muscles, etc...). Some disorders affect only one part of the body, while other diseases are generalized, affecting many muscles.