Migraine is a neurological disease characterized by recurrent moderate to severe headaches often in association with a number of autonomic nervous system symptoms. The word is derived from the Greek ἡμικρανία (hemikrania), pain on one side of the head, from ἡμι- (hemi-), half, and κρανίον (kranion), skull. Chronic migraine is a complication of migraines, and is a headache that fulfills diagnostic criteria for migraine headache and occurs for a greater time interval. 2  Specifically, greater or equal to 15 days/month for longer than 3 months.