Hi Ronald,
I don't know exactly what approach you are using, but as others have said, this is reasonably common.
Mahasi Sayadaw,
Practical Insight Meditationhttp://aimwell.org/Books/Mahasi/Practical/practical.html
Should you intend to sway the body, then knowingly note intending. While in the act of swaying, swaying. When contemplating you may occasionally discover the body swaying back and forth. Do not be alarmed; neither be pleased nor wish to continue to sway. The swaying will cease if you keep the knowing mind on the action of swaying and continue to note swaying until the action ceases. If swaying increases in spite of your making a mental note of it, then lean against a wall or post or lie down for a while. Thereafter proceed with contemplation. Follow the same procedure if you find yourself shaking or trembling. When contemplation is developed you may sometimes feel a thrill or chill pass through the back or the entire body. This is a symptom of the feeling of intense interest, enthusiasm or rapture. It occurs naturally in the course of good contemplation. When your mind is fixed in contemplation you may be startled at the slightest sound. This takes place because you feel the effect of sensory impression more intensely while in a state of concentration.
I had some moderate shaking (actually mostly swaying) for a few days on a retreat last year. My teacher was a little concerned that I might injury myself (by falling on something, especially if it happened while doing walking practice) but apart from that assured me that it would pass. He said he'd seen people sway so violently that they banged their head on the floor!
I know nothing about the theory behind stuff like kundalini (I've stuck mostly to Buddhist teachings) but I've noticed that often when I've had these sort of involuntary motion things that they seem to be the body kind of straightening itself out, getting rid of some sort of habitual bad posture that is causing cramping or pain, and eventually getting itself into a proper , comfortable posture (after possibly going through a bit of pain to get there...).
Mike