Torticollis comes from the Latin for "twisted neck". Acute torticollis is a sudden onset of neck pain and stiffness, often with the head held tilted or rotated to one side because moving it the other way is too painful. The muscles on one side of the neck go into a protective spasm, which is what creates that locked feeling.

It tends to appear overnight or come on quickly during the day, sometimes after an awkward movement, and sometimes with no obvious trigger at all.