The Norwegian-born Joly "was hospitalised in the cardiovascular department of Cochin Hospital at 2.30am on Monday morning after a fall with facial trauma and brief loss of consciousness," medical officials said.
"There are several superficial bruises to the face and the right eyebrow," it said.
Checks for heart problems proved negative, suggesting that Joly had tripped rather than had a heart attack, they added.
She was released on Monday evening and returned to her home in the Montparnasse area of the city, her party said.
Opinion polls say that Joly, 68, who worked previously as an investigative magistrate, is on course to win around two percent of votes in the April 22nd first round of the French presidential election.
Under the terms of the constitution, if doctors had identified a serious health problem that would have affected her ability to campaign, the election could have been postponed by up to 35 days.
As it is, her campaign director Stephane Sitbon-Gomez said Joly's fall had had no direct effect on her campaign and she would be attending an election rally in the western city of Nantes on Wednesday as scheduled.