On Sunday, she fell ill at Ground Zero and was forced to leave the 9/11 memorial ceremony in New York early.
The former secretary of state has been experiencing a cough related to allergies.
Hillary Clinton was on Saturday "voluntary" quizzed by US federal prosecutors for three and a half hours as part of a probe that has hung over her White House bid for her use of a private email server as secretary of state.
Hillary is accused of having made "false and defamatory statements negligently, recklessly and purposefully and/or intentionally with malice" in her public comments, including those about the connection between the attack and an anti-Muslim YouTube video.
Democratic presidential frontrunner Hillary Clinton will hand over her private email server, she used while serving as secretary of state, to the United States justice department to cooperate with the government's security inquiry.