Julie Matthias’s family have a game they sometimes like to play after she comes home, disappointed, from another doctor’s appointment. During dinner, they pick a foreign accent, and challenge each other to speak in the strange voice.

The playful jokes help to distract from the distress of a condition that her doctors have struggled to treat. Despite having lived in the UK her whole life, Matthias suddenly found that she no longer speaks with an English accent – sounding French or Chinese instead. “Four years ago this Easter – that was the last time I heard my own voice,” she tells me on the phone.

Matthias is one of a handful of people in the UK with foreign accent syndrome. Although their speech is completely fluent, their voices have somehow taken on odd characteristics that make them sound as if they grew up in another country.

The causes are complicated, and sometimes puzzling to scientists. Matthias thinks her experience can be pinned down to a car accident that was followed by blinding migraines, often accompanied by debilitating body pain. “It feels like your brain is going to explode,” says Matthias. “Your joints are so tender, so painful, you feel you can’t breathe, you can’t get the air in… I’d rather have more babies than go through that pain again.”

Hear Julie Matthias’s accent in an interview with BBC News

Then, a few months after these painful episodes started, something even stranger happened. Her voice started shifting accent. The change soon caught the attention of people in her beauty salon. “Clients talked to me as if I didn’t understand English.”