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.
1 Worsening of symptoms in the evening. 2  Symptoms occur mainly at night. 3  Nighttime leg twitching. 4  RLS/WED may be associated with another, more common condition called periodic limb movement of sleep, which causes your legs to twitch and kick, possibly throughout the night, while you sleep.