A migraine is an intense, throbbing headache that may be accompanied by nausea or dizziness. A migraine can last from hours to days. Much about migraines isn’t understood. Many researchers believe that a migraine can be caused by a change in hormone levels in the brain. Migraines can be triggered by stress, bright lights and certain smells. They can also be caused by medications, and by getting too little or too much sleep.