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.
Another theory suggests that as youâre drifting off to sleep, your brain misinterprets the relaxing of your muscles as a sign that youâre actually falling and signals your muscles to tense up, in order to protect you. More often than not, hypnic jerks are nothing to worry about. If one wakes you up, simply roll over and go back to sleep. But keep in mind: a high caffeine intake, strenuous evening activities, emotional stress, or sleep deprivation may increase the frequency and intensity of hypnic jerks.