It’s not uncommon to experience slurred or delayed speech following a stroke or brain injury. Some people, however, develop foreign accent syndrome, or FAS, as reported by the University of Texas at Dallas. This condition, which has also been linked to multiple sclerosis and conversion disorder, makes people use tempos and intonation that are different from those found in their native dialect. People with this disorder may change the way that certain letters are pronounced, stress different syllables or alter the rhythm of their speech, but they sound completely intelligible otherwise.
Although the first recorded incidence of FAS was documented in 1907, The Atlantic says that the current name for the problem was coined in the 1980s.
More recently, one Texan woman experienced FAS several times after falling asleep with an intense headache. Each time, she awoke with a different accent.
This seems humorous, but experiencing changes in the way that you sound can be psychologically debilitating. A new accent can alter your identity.
Smithsonian.com explains that FAS can be caused by neurological damage or psychological disorders. In the case of the Texan woman, doctors attributed the malady to a specific type of migraine headache.
There have only been about 100 documented cases of the condition, and many neurologists are skeptical about its validity. Doctors who have worked with patients with FAS say that it is a very real speech disorder.