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.
Nerve misfiring: One hypothesis for the hypnagogic jerks is that they are an inherent aspect of the bodyâs transition from wakefulness to sleep. This hypothesis suggests that as we transition to a sleeping state, our nerves may occasionally misfire, causing a jolting movement immediately before weâre fully asleep.