Dim Mak also know as "touch of death" is an ancient Chinese art that uses body energy, acupuncture points, and meridian energy for a self defense purpose. The word "dim mak" roughly translates to "push artery." Therefore Dim Mak also works by striking the vascular system of the body.
Over the last 30 or so years Dim Mak has polarized the martial arts into the believers and those who disbelieve. Here is a link to an article on this from Black Belt Magazine.