Don't be scared Lee,
it can be related to stress, medicine etc.
Here is couple lines from one web page, please don't panic about it
"Call your doctor if:
Your tremor is worse at rest and gets better with movement, like when you reach for something.
Your tremor is prolonged, severe, or interferes with your life
Your tremor occurs with other symptoms, such as headache, weakness, abnormal tongue motion, muscle tightening or contractions, or other movements that you cannot easily control."
As your writing is essential to you and as well to some other survivors form MS, please think about medical check. Don't be scared because of that. It is nothing, just regular check... And we all need you capable of writing, so if there is some tool under your arm to make it easy why not try to take it. Please don't panic but think on calling or talking with your doc about it..