Without seeing the movement, I can only speculate on this, but if the head nods are done repetitively, then it might be a tic. My son was diagnosed with epilepsy first, but also showed signs of tourettes during the evaluation. He has developed numerous tics, one of which was head nodding. Again, I don't know if the movement you're describing is epilepsy related or tic related, but thought i'd throw my two cents in.

My family tells me that I nod my head ever so slightly when I am watching TV or looking at the paper or talking to people. I don't know I am doing it. I ask them to tell me when I am doing it so I can see if a pattern is occurring. I am not nodding to music or in approval of what people are talking about, it is an involuntary movement so it seems that will annoy my family and I don't even know I am doing it. Couple that with my eye twitch when I sneeze? What is going on? Anyone have any ideas? I am 52 female and healthy, just curious why my head wants to move and I don't know about it? Thanks.