Nightmare Protection

I met a bloke today who showed me this amulet hanging around his neck. He had carved it from a stone he found on a beach. He explained that it's in the shape of a stylised axe to ward off nightmares.
When I got home I looked up nightmares in A Pocket Guide to Superstitions of the British Isles which states that in 1564, Thomas Blundeville of Norfolk described a 'fonde foolishe charme' to prevent nightmares involving a holed stone to be hung over the sufferer's bed.
Plus ça change.