Mrs Clinton seemed to buckle while waiting to get into a minivan at a ceremony to mark 15 years since the 9/11 terror attacks in New York, and she needed help from her security detail.
However, in a phone interview with CNN, the Democratic candidate said she became dizzy but did not lose consciousness.
The 68-year-old said she felt immediately better after getting into her air-conditioned vehicle.
In the interview she admitted she had earlier been diagnosed with pneumonia and was told to rest for five days.
But she admitted not following “that very wise advice”.
Mrs Clinton’s campaign team has said it will release more of her medical records following the incident and admitted being too slow to provide information about her condition.
News Source SkyNews