Sarkozy collapsed on Sunday while jogging in the wooded parkland around the Palace of Versailles just outside Paris, the French capital.
His bodyguards and his official doctor, running alongside him, were able to help him lie him down.
His wife, Carla Bruni, raced to the scene of the incident on a police motorbike, a witness told the AFP news agency.
Sarkozy, who assumed the presidency in May 2007, is a fitness enthusiast, and is often seen jogging or cycling with aides and bodyguards.
Just over three weeks ago, the Elysee Palace released the findings of Sarkozy's latest annual health check, describing the results of recent blood and heart tests as "normal". No further details were provided.