My wife would probably have a better response than I, as she is better at dodging flying arms and legs...
It very well could be rythmic movement disorder - more common in younger children, and less common in adults. When I joined the Navy in the 80's, some of my shipmates went and got the medical folks, because they though I was having a seizure...
My wifes approach ranges from giving me a wide berth to a flat out "wake your rocking butt up"...I've heard there are meds nowadays to help...