in turkey, Prof. Ersin TAN published an article about using mexitiline, as you know, mexitiline is used for arranging the rhtme of heart, so if you use another purpose, according to his article, you have to be under monitering.
Tremors are a common side effect of Mexitil. Are you on a higher dose than before?
The other medication you can check is Lamictal (lamotrigene). They have that in Germany. It helps with myotonia and it has an anti-anxiety effect like Lorazepam.