I had similar experiences a few years ago, not long after I had started meditating.
In my case, I saw them as something interesting. At times it bugged me or frightened me too. It is pretty interesting how the body can do nontrivial and intelligent things without your help. Nowadays it happens a lot less (beyond the body 'just' settling into meditation which is in itself an interesting process), and it seems like I have to allow it to happen
What I would suggest is to pay attention to your mental attitudes towards the phenomenon. For instance, as freaked out as you may be, you may also be finding it subtly pleasant, titillating, fascinating, a sign of progress, etc. etc. Those are good things to note.
Another possibility is to resolve for there to be no movements of the sort you're describing and to actively but calmly come back to your concentration practice and intended posture when they begin.
Otherwise it seems pretty harmless provided that you're not buying too excessively into the idea that your body has special self-healing powers (which may lead to making bad decisions about length or intensity of practice, for instance).
To editorialize a bit: I see no need at all to change your world view to include spirits and entities and whatnot (at least not from what you describe

. Though that may be your inclination, of course.