President Sarkozy was flown to hospital after he had collapsed in the park of the Palace of Versailles.
The president is on a diet and exercise regime had gone for a run in hot weather and it appears he overdid it.
Officials at the Elysee Palace have rejected earlier reports that Sarkozy had lost consciousness but claim that he had to lie down.
A doctor who stays with President Sarkozy at all times gave him first-aid treatment and then called for a helicopter to take him to hospital.
Sarkozy was diagnosed as suffering a vasovagal syncope, according to the AFP news agency.
He is expected to make a full recovery and is taking some time off to recuperate.
