I completely believe in this kind of thing. When I was very little..like seven or so, I remember sleeping on my stomach and feeling this hand on my back. I wasn't afraid and I just KNEW it was my grandmother..who died when MY mom was three so we never met. I just knew it. I turned and no one was there.
I do think that kids are much more in tune with this sort of spritual world. I think it explains alot of "imaginary" friends.
The shaking would worry me that I was being warned of something. Maybe if you know to expect it you might put the thought in your mind to "see" what it means..beyond the fear.
I love this kind of stuff