She's now recovering at home and being monitored by doctors.
An aide, Philippe Reines, says Clinton will work from home next week, at the recommendation of doctors.
Congressional aides do not expect her to testify as scheduled at congressional hearings on Thursday into the Sept. 11 attack against a U.S. diplomatic outpost in Benghazi, Libya, that killed four Americans, including the U.S. ambassador.
The aides spoke on condition of anonymity because they weren't authorized to publicly discuss Clinton's status.
The department says Clinton was dehydrated because of the virus and that she fainted, causing the concussion. No further details were immediately available.