A serious migraine can lead to nausea, sensitivity to light and even temporary paralysis of limbs, but for one woman it resulted in a foreign accent.
Kay Russell, 49, went to bed with a severe migraine and when she woke up found she was speaking with a French twang.
The grandmother, from Bishop's Cleeve near Cheltenham, is thought to be one of only 60 people in the world known to suffer from foreign accent syndrome, a condition which damages the part of the brain that controls speech and word formation.
They believe it is triggered when tiny areas of the brain linked with language, pitch and speech patterns are damaged.
Speaking to the Gloucester Echo, Mrs Russell said: "As a sufferer of this syndrome, you are not trying to speak in an accent, it is a speech impediment.
"Whatever accent you hear, it is in the ears of the listener."
Mrs Russell is most commonly mistaken for French or eastern European.
She continued: "It also affects my hands and makes me write with a foreign accent. For example, I say "peoples", not "people", and that is how I would write it.
"You lose your identity and an awful lot about yourself. I feel like I come across as a different person."
She has suffered with migraines for 20 years.
After one bad migraine she was left with slurred speech for two weeks and made an appointment to have an MRI scan and see a neurologist.
Then on January 4 she woke up with a French accent.
Foreign accent syndrome can last for days, weeks, months, years or forever, and there is no known cure.