Why does my head involuntarily move back and forth?

I have recently started having seizures. Mine aren't the same as your symptoms, but I've done a lot of research. That is what is sounds like to me. A seizure doesn't have to be shaking or convulsions or falling out in the floor. You should do a little research on line and then think about seeing a neurologist. Some of my symptoms I had not even noticed until my dr pointed them out to me. I hope that helps!