Unilateral headache and the behaviour of unilaterality underpins diagnostic criteria in the medical classification of headache. However, the medical model of headache admits to a lack of understanding of the mechanism of unilateral alternating headache. A (medical) attempt was made in the late 1980s which hypothesised involvement of (intracranial) structures in or closely adjacent to the midline, with the pathologic state being duplicated contralaterally as it spreads across the midline. Alternating side-locked headache mimics alternating lateral lumbar list / shift which is thought to be a result of alternating aberrant lumbar intra-discal behaviour; could C2-3 intra-discal disc behaviour be responsible for alternating headache? My clinical experience suggests that it is responsible. Undoubtedly though, lumbar and cervical discs are structured differently, which suggests extrapolation from lumbar to cervical discs is tenuous. However, this review of contemporary research, which dispels widely held beliefs of intervertebral cervical (and ageing of) discs, not only supports, but strengthens my hypothesis.