I don't suffer from internal tremor, but there have been some posts around the web and forums that taking a magnesium supplement is helpful. I take magnesium citrate and find it helps me sleep and reduces my fidgets between doses of medication. Please be aware that the usual tablets of magnesium citrate are absolutely enormous. I found them very difficult to swallow. It may say each tablet contains 200mg of magnesium, but I weighed one on some small scales and it weighed 1.7 grams. I take magnesium citrate as a soft gel. They are still huge, but they are easier to swallow.
Good luck.