Off your rocker

Origin

The image of a rocking chair, steadily swaying back and forth, evokes a sense of calm and predictability. But what happens when someone literally falls or slides "off their rocker"? They become unstable, unbalanced, perhaps even tumble onto the floor in an undignified heap. This clear visual of physical disequilibrium gave rise to the phrase. Sometime in the early 20th century, the literal instability of a person coming off their rocking chair became a potent metaphor for mental imbalance. Just as the chair's occupant had lost their steady base, so too had the person's mind, slipping into erratic, unpredictable, and downright crazy behavior.