Migraine headaches result from a combination of blood vessel enlargement and the release of chemicals from nerve fibers that coil around these blood vessels.[3] Some people who suffer from migraines can clearly identify triggers or factors that cause the headaches.[2]A migraine headache causes the sympathetic nervous system to respond with feelings of nausea, diarrhea, and vomiting.[3] Migraines may be caused by changes in the brainstem and its interactions with the trigeminal nerve, a major pain pathway.