I have noticed Apache toss his head a bit of the last 7 months or so but I have no idea why he does it.
He only does it occasionally sometimes he will do it all day every few seconds, others he maybe does it twice all day and there can be weeks between the days of head tossing.
The first time he did it he had some bad scratches on his nose and there were flies that we thought were annoying him. The second time he still had the scratches and he was eating hay, so I thought maybe it was poking his nose.
But now I realise he does it standing in the paddock, eating, being led, being ridden etc. On his bad days I don't like to ride him because I constantly have the reins/leadrope pulled out of my hands, though he never takes advantage of this. He acts like something is anoying him and he is tossing his head to get rid of it.
He rarely does it and when he does it is impossible to get him to stop. It is really annoying me because I don't know what to do about it. Today was his worst day because at times he was even getting his front legs involved a couple of times like he was striking which he never does.
I don't have a video of him but this video shows a horse doing the same thing a lesser extent.
Apache is a bit more violent/sudden about it and it is much more obvious when he chucks his head up.