He did this twice yesterday: banging his forehead on the banisters till he cried and then, later, the back of his head against the wall, also until he cried.
He was pretty shattered and going down with a cold (not swine flu), but not being ignored or otherwise seeming to be in distress. He's usually pretty cheerful, very cuddly and tactile and physically very strong and resilient.
Anyone experienced this behaviour?