Actually the 'why' is somewhat hazy, and is one aspect which does not seem to correspond to any dislocation of sorts. I cannot recall one instant in which my foot suddenly 'went', but it also was definitely not a gradual onset either. All I remember is sitting on a grassy hill, getting up and sort of realizing that it hurt. This was shortly after my course walk, and just prior to warming up. Could it be possible that overuse had put my foot on the verge of the injury, and getting up quickly was the 'feather that broke the camels back' as they say? What exactly would a tendon 'misfiring' be? Is there a medical term for it? How is it treated?