Hillary Clinton, the US secretary of state, sustained a concussion last week after suffering from extreme dehydration and fainting while suffering from a stomach virus, the state department has said.
"While suffering from a stomach virus, Secretary Clinton became dehydrated and fainted, sustaining a concussion," Philippe Reines, a US State Department spokesman, said in a statement on Saturday.
"She has been recovering at home and will continue to be monitored regularly by her doctors," Reines said, adding that Clinton would work from home and stay in regular contact with other top officials.
Clinton, 65, is recovering at home and has been advised by her doctors to continue to rest and avoid strenuous activity and cancel all work events for the next week.
She had been scheduled to testify before a pair of congressional panels looking into the September 11 attack against a diplomatic outpost in Benghazi, Libya.
Clinton's concussion was suffered on Thursday, after she fainted at home earlier in the week, a state department official speaking on condition of anonymity said.
Clinton, who is expected to leave her job soon, skipped an overseas trip this past week because of the stomach virus, the State Department said.
President Barack Obama telephoned his top diplomat Saturday to wish her well, a White House official said.
The State Department said in a statement that Clinton will continue to work from home in the week ahead and looks forward to returning to the office "soon", the statement said.
William Burns and Thomas Nides, both senior state department officials, will stand in for Clinton at the hearings in Congress.
Clinton backed out of a trip to North Africa and the Arabian Gulf on Monday because she was sick. She caught the virus during a recent visit to Europe.