Excellent question. Thank you.
What you are talking about is a certain inertia you are creating within your system. As you sit and allow stillness to come within you, your life energies can move more freely within you. As this happens many make sounds, movements, eyes roll freely, body moves seemingly at will. Seemingly random twitching and jerking of some body part happens. This means you have consciously made yourself in such a way that the plane of inertia within your body is open to more energy and movement happens. It only feels as though you aren’t doing it because it is a new experience. But you chose to sit and make yourself this way. This is good. You are flowering. Yes. Growth is happening within you. Embrace this and simply allow yourself to watch it happen. Not with your eyes. But with your internal eye. When your eyes are closed you still see. Isn’t it? You see that body moves through the sensation of movement. This sight is confined to the inner boundaries of your body at first. But as your awareness grows energy body expands. As it existed your boundary of what is you expands. As this happens you experience a far bigger piece of life as you. These sensations you experience are your life energies expanding. Growing. Old mind patterns will try to tell you it’s no good. This is ego worrying about what happens to me? This Is energy and emotional talk within you this happens. Watch these as well. Watching means allowing it to be there and happen without becoming that emotion. You feel it but it does not become your mood. It is left to feel more like an itch you scratch and it goes away. You do not become the itch and go crazy over it. You scratch and it goes away. You may need to scratch a few times but it goes. Gone. Not one more sensation or thought comes about it. It just goes away and you let it. These thoughts are the same thing. Let them be there. Then let them go.
Perhaps look at what happens during sex for a dramatic example of intense energy moving in the system. Once energies hit their peak as matter is created from energies being highly excited, full body twitching happens. Shaking and twitching of bliss and ecstasy happens. Isn’t it? Because you did some action that allowed you to rev up the pitch of your energies, you create life making material that feels like bliss and body does things as energies move. Isn’t it so? Yes. Sitting to become still is another way of creating this inertia for energy to move. Freedom of flow. It just comes from a state of stillness and not action to increase intensity in life creation mode. Regardless of how you label these two sensations in your mind, the same sensations are felt within you. One more intense than the other that is subtle. You can sit and pitch up your energies in just the same way as sex if you choose to. There is a name for this too that has a certain negativity around it. But the point is that you can and do control your own life energies. Sitting, hugging and kissing or otherwise, you control your energies. Isn’t it?
Meditation can be seen as a tool for exploring ones own energies. Experiencing the sensations created within the body to see that all sensations are the same. Your energy moving through the body. Only a human mind condition of ego uses intellect to cut these into different energy sensations. Fundamentally they are the same. Just different pitches or frequencies.
I hope this helps.