This sounds incredibly similar to me. When doing stomach crunches and I hold my body in one position for a number of seconds, I start to shake uncontrollably MUCH more that the average person.
When lifting heavy weights at the gym, my arms shake at the elbows so much people sometimes notice, my friends have also affectionally nicknamed me Parky. I also experience tremors in feet, hands, lips and tongue, all the time when they are held in certain positions.
This has been going on for some time now, which has led me to rule out any serious neurological diseases such as MS or ALS, as other symptoms would have occurred by now.
True, it could be Mercury, as I do have six amalgam fillings at the moment. But I’m certainly not going to place all my hope on that, I’m simply going to remain open to the possibility that I COULD be mercury poisoned.