This term refers to a frightening sensation of being held immobile in bed, often by a heavy weight pressing on one's stomach or chest. It is now recognized medically under the name ‘sleep paralysis’; it can be accompanied by the sense of an alien presence, and by visual hallucinations. In folklore, it was thought of as a magical attack, though whether by demonic incubus, ghost, harmful fairy, or witch varied according to place and period. Where the term ‘hag-riding’ was used it usually implied that a witch was to blame, and in 19th-century Dorset and Somerset several people were prosecuted for physically attacking elderly women who, they alleged, had ‘hagged’ or ‘hag-ridden’ them, in order to break their power by drawing blood (Davies, 1997: 37–9).
The commonest counter-charm was a holed stone above the bed; however, one Somerset man in 1862 slept with a nail-studded board tied to his chest, so that if the hag who had plagued him came again, ‘she won't sit there long!’ (Davies, 1997: 47). A Hampshire woman used to hang a scythe over her children's bed (N&Q 10s:7 (1907), 157).
When horses were found sweating and exhausted in the morning, it was thought that witches or fairies had ridden them all night, and tangled their manes; this too was called hag-riding, and could be prevented by hanging a holed stone over their stalls, round their necks, or at the stable door. Hooks and shears were effective too (Herrick, Hesperides (1648), no. 892).