I'm with R41 -- 40 was the beginning of being middle-aged.. But my 50's have shown me it really is the beginning of the end. I had an sports injury @ 50 that made it difficult for me to exercise, and I put on 20 lbs. The knee surgery I had to try to correct it only left things worse.
According to the National Institute of Neurological Disorders and Stroke (NINDS), the sudden, involuntary jerking of a muscle or group of muscles while drifting off to sleep is called myoclonus. It is caused by sudden muscle contractions, also known as positive myoclonus, or muscle relaxation, which is referred to as negative myoclonus.
Often, patients wake up to find their affected finger or thumb in a locked flexed position, which creates a restless sleep pattern. Furthermore, trigger fingers and thumbs creak upon flexion and extension. The cause of trigger finger or thumb is repetitive movement, with increased degrees of motion, time and clenching.