I experience them frequently. It feels as if your entire body is vibrating inside, and there is nothing evident on the outside. It's just this internal shaking! I have a PD.and I feel it originates from that. I assume you haven't, as you did not mention it in your post - when I get it usually passes in an hour. It comes about mainly in the mornings as soon as I wake up. It is annoying, and it feels that I am ultra-sensitive to any stimuli that wreak havoc with my nervous system. Do yoga and ground yourself. Iyengar yoga works for me. It's all about grounding and holding each pose for a long time, which keeps the internal body strong. Calm. I hope this helps.