It probably appears only when you try to carry specific tasks.
Unless your focal dystonia have developed into a severe case where you can feel your symptoms over the whole course of your sleep cycle (I not even sure if there is such case...) the symptoms should only appear as a response to certain stimuli.
It is much like having a switch to turn your focal dystonia symptoms ON and OFF. They come "ON" with stimuli associated with playing the instrument, such as being in contact with a keys and pressure the keys. Other variables include changing positions, opening the hands, the thought of a movement, hearing certain sounds, feeling certain emotions, feeling gravity in a different area of the body and even tasks that are not related to instrument playing. Most of the time the switch is turned "OFF".
The point of recovery where we want to be is ....
TO BE ABLE TO PLAY THE INSTRUMENT WITH FOCAL DYSTONIA SWITCH TURNED OFF AT ALL TIMES or MOST OF THE TIMES.