84 year old father, has been taking 1/2 Ambien each night to aide sleeping, for about the last two weeks. Last night he did not take a dose and slept reasonably well. This afternoon and into the evening, he is experiencing muscular tremors throughout his body as if he is shivering from being cold. He is not cold and the tremors are annoying but not uncomfortable. Is that a possible side effect? To complicate a diagnosis, he is severely arthritic, mostly non ambulatory except for moving himself from chair to wheel chair to bed to chair etc- with assistance. Also is on dialysis 3x week for full kidney failure. Any thoughts?