The headaches began after the patient entered a 'head shaking contest' with his peers. The object of the contest was to vigorously rotate the head back and forth for as long as one could tolerate. The patient won, with a time of approximately 2 min. Afterwards he noted a mild headache that gradually worsened over the course of 2 weeks. When it was at its most severe, the headache was occasionally accompanied by nausea and vomiting.

via Mind Hacks: Head shaking competition.