See subject. Maybe it’s just me.
If it’s a morning thing, could it be a “haven’t used my muscles in a long time” thing?
I’ve noticed the phenomenon now and then throughout the day.
Can’t offer too much helpful other than to say that its not just you. I do the same thing. It drives my wife nuts.
Wild speculation would be that it the process of stretching my muscles I put them at odds with eachother and into an unstable equilibrium. Against this idea is that I can make a conscious effort to resist it in my upper body (as when I’m cuddled up with Mrs. Godot.) but then it comes out in my legs shaking.
Dogs do it. Bees do it. Even little flees do it. We all like to stretch in the morning. My initial reaction is way more dynamic than a mere quiver. My muscles spasm in reverse of the stretch and it’s almost enough to throw me across the room.