Banging his head is just something tups do, Soay more than other breeds. He might have damaged his neck doing this. It's a good idea with head bangers to bash a stob deeply into the ground somewhere so he can smack that and can also use the squared edge to scratch between his horns. Another use for willow branches (after they have eaten the bark off) is to scratch in awkward to get at places
There may also be neurological conditions which could cause the head raising - sorry I don't know the precise symptoms
If your tup has served all his harem and they are now in lamb, he will have no reason to service them any more. Also, Soay are very seasonal breeders and we are no longer in the rutting season. In nature, he would now move back with a batchelor group for the spring and summer, and leave the ewes in peace.