The 54-year-old president, a keen runner and cyclist once nicknamed "Speedy", was kept under cardiological observation in the Val-de-Grace military hospital overnight after he stumbled and felt faint during his Sunday morning run with a team of bodyguards at La Lanterne, his weekend residence in Versailles.

A witness walking in the gardens of the Sun King's palace leading to La Lanterne said he saw the President running with his guards. He looked "tired" and suddenly fell over.

Mr Sarkozy's wife, Carla Bruni-Sarkozy, 41, rushed to the scene on a scooter, the witness said.

Two helicopters landed in the woods shortly afterwards, and Mr Sarkozy was transported to the hospital in Paris.

Advisers said he had suffered a "minor vasovagal episode" - a problem with the vagal nerve in the brain which slows the heart rate and blood pressure and can occur during exercise. He was expected to have further tests.

"He had this problem when he was exercising, jogging. He has come round," said Claude Guéant, Mr Sarkozy's chief of staff.

"The president is totally conscious, his episode did not last very long. He's doing well and talking normally to medical staff."

Mr Sarkozy’s aides said there were no plans to cancel his visit on Tuesday to the Mont Saint Michel abbey in Normandy.

“He’s fine. He’s hungry. He’s complaining. Everything’s going well,” said his friend Patrick Balkany after talking to Mr Guéant and Mrs Bruni-Sarkozy.

“Carla reassured us straight away ... it’s a passing thing. The president is going to have to take more care, work a little less hard and eat a little bit more,” he added, saying that a diet he said Mr Sarkozy was on to lose weight was part of the problem.

“Recently the president has looked very honed, he looks more like a Tour de France rider than a president,” he joked.

Mr Sarkozy's wife was at his side last night, while François Fillon, the prime minister, returned to Paris from his constituency.

Roselyne Bachelot, the health minister, said the episode was "small" and that she was sure that president had managed to watch the final leg of the Tour de France on television in his hospital bed.

Last night, the Val-de-Grace hospital was guarded by police and secret service agents and there were metal barriers around the entrance.

Mr Sarkozy promised during his campaign for election that he would be more transparent about his health than his predecessors – several of whom concealed their ailments.

However, he was widely criticised when it was recently revealed that he had been secretly admitted to the same hospital the day after his divorce from his second wife, Cecilia, almost two years ago.

On Oct 21 2007, doctors at Val-de-Grace treated him for a high fever and a throat abscess. The president underwent surgery to remove infected material, was given antibiotics through a catheter, and then discharged.

His stay was only revealed three months later.

He last underwent a medical examination July 3, when his cardiovascular and blood tests were normal.

The late Socialist president François Mitterrand promised to release information about his health, but it later transpired that he had hid the fact that he had cancer from the public.

Mr Sarkozy is a fitness fanatic who neither drinks nor smokes – bar the odd cigar – and whose high energy levels have won him the nickname of "speedy".

Photos of "Super Sarko" jogging down the Elysée steps in a tracksuit on day one of his presidency bolstered his high-octane image. But following criticism that such sights were undignified, he now takes his daily runs in the gardens of the presidential palace.

Mr Sarkozy also has a personal trainer who has helped him lose around 9lb and two trouser sizes.

Julie Imperiali, 26, who specialises in strengthening the pelvic floor, said earlier this year that she had helped the president get more in touch with his body as before he "he used just to run and run and run without being aware of his body".

A vasovagal episode is the dilation of the body's blood vessels in response to stimulous from the vagal nerve, which is responsible for bringing down the heart rate and arterial pressure.

It can lead to a temporary loss of consciousness but usually is not serious. It can be caused by intense exercise when it is very hot, as well as by extreme emotion, stress or dehydration.

In Paris on Sunday humidity was high and temperatures were up to 28 degrees Celsius.

"This (vasovagal episode] sounds like a consistent version of events, but for a man of that age, there lot of other things it could be," said a medical source. "More tests would be needed."