A migraine is a headache that is long-lasting. Pain is usually felt to one side of the head and around an eye. Nausea, vomiting and dizziness may also be symptoms. Before a migraine begins, may people experience auras, which are disturbances in vision such as flashing lights or dots. There may be many reasons why a migraine is triggered, such as food intolerances, hormonal changes, the environment, and stress.