Ever since I can remember, if i move my head/neck quickly and in a particular but unreproducible way, i get this indescribable pain shooting up the back of my head and round the side of it. It makes my face grimace in agony, and it makes me cry and feel really sick. The pain lasts about a minute and gradually ebbs away. Once it's happened, it's likely to recur in the next few hours but then it'll go away for months at a time.
Just now, my DS (age 8) was in a strop with me, and flung his head round to shout and i saw the exact same thing happen to him. He was horrified, and screamed and cried for ages. What is it? Are our heads wired up wrong?