Secretary of State Hillary Clinton, who cancelled an overseas trip last weekend because of illness, suffered a concussion after fainting due to dehydration, prompting the postponement of her scheduled congressional testimony on the attack on a US mission in Libya, officials have said.
"While suffering from a stomach virus, Secretary Clinton became dehydrated and fainted, sustaining a concussion," State Department spokesman Philippe Reines said in a statement.
"She has been recovering at home and will continue to be monitored regularly by her doctors.
“At their recommendation, she will continue to work from home next week, staying in regular contact with department and other officials. She is looking forward to being back in the office soon," Mr Reines added.
Mrs Clinton fell ill with a stomach virus last weekend and was forced to cancel a planned trip to the Middle East and North Africa.
The virus also hit other members of her staff, who were returning with her from a European trip, and was described as uncomfortable, but not medically serious.
Ms Clinton, 65, has often been cited as a potential candidate for the US presidency in 2016 and frequently refers to her general good health, saying in an interview with ABC broadcast that she has "incredible stamina and energy."
She has maintained a punishing schedule in her final weeks as the top US diplomat, a position she intends to leave toward the end of January when US President Barack Obama is sworn in for a second term.
Ms Clinton had been expected to testify on 20 December before the House of Representatives and Senate foreign affairs committees on a report on the deadly attack on the US diplomatic post in Benghazi, Libya, that killed the US ambassador and three other Americans and raised questions about security at far-flung posts.