After suffering from a stomach virus, then-Secretary of State Clinton fainted and struck her head. From the New York Times in December 2012:
Secretary of State Hillary Rodham Clintonsuffered a concussion early last week after fainting and striking her head, the State Department disclosed on Saturday. * * * The fainting episode occurred after Mrs. Clinton, who is being widely discussed as a possible presidential candidate in 2016, became dehydrated because of a stomach virus she contracted during a trip to Europe, according to statements released by a close adviser and her doctors.
One State Department official said Mrs. Clinton fainted when she was alone at her home in Washington but added that the concussion was not diagnosed until Thursday. He said the concussion was not severe.