He is known as Speedy Sarko, a ball of energy who leaves ministers and officials gasping at the pace of his reforms and the density of his schedule. His image is athletic, virile and ruthless — that of a man in a hurry who pauses only to win the hand in marriage of Carla Bruni, the glamorous model and singer.

Yesterday President Sarkozy’s all-action programme came to a halt as he fainted while jogging in the grounds of his weekend residence in Versailles. He was taken by an army helicopter to Val-de-Grâce military hospital in Paris, where he underwent a series of tests. Ms Bruni, 41, was seen arriving at his side on a motorcycle before accompanying him to hospital.

An official said the supposedly indefatigable head of state, aged 54, had suffered a minor vasovagal episode — a loss of consciousness which can be provoked by such causes as hyperthermia, dehydration or stress.

Professor Xavier Jouven, a cardiologist at Georges Pompidou Hospital in Paris, said such episodes were caused by a fall in arterial pressure and heartbeat frequency. “The two together mean you get less blood going to the head, you don’t feel well and you need to lie down.

“It’s benign, it’s frequent and it’s common with sportsmen just as they end their physical effort.”

Claude Guéant, general secretary of Mr Sarkozy’s private office, said the President was “well” and “talking normally with carers” at the hospital, which was cordoned off by police. Mr Guéant appeared to rule out a heart attack as the cause of the collapse, although doctors said further examinations would be necessary before giving Mr Sarkozy a clean bill of cardiovascular health.

“He’s OK, he’s hungry, he’s complaining,” said Patrick Balkany, a member of Mr Sarkozy’s Union for a Popular Movement.

The Elysée Palace said that a blood and heart analysis carried out during a regular check-up on Mr Sarkozy this month had produced “normal results”. In a statement last night, the Elysée denied reports that Mr Sarkozy had fainted, and said he would leave hospital today.

A keen jogger who has employed a personal trainer, the President runs for at least an hour several times a week. He is also an enthusiastic cyclist. He was finishing a 60-minute run in the company of his security guards in warm sunshine shortly after lunch when he passed out, according to a French government source.

A witness said she had seen Mr Sarkozy stagger and collapse in the grounds of the Lanterne, the state-owned mansion in Versailles used by France’s presidential couple.

He was treated by his personal doctor before being taken to hospital, according to a statement from the French presidency.

François Fillon, the Prime Minister, rushed back to Paris from a weekend at his rural home in central France to avoid the risk of a power vacuum at the heart of the French state.

Doctors warned that tiredness could be a factor in the presidential malaise, especially given Mr Sarkozy’s notorious reluctance to interrupt a gruelling timetable to rest. In the last week alone, for instance, “l’hyperprésident” travelled with Ms Bruni to New York for Nelson Mandela’s 91st birthday concert and followed an Alpine leg of the Tour de France — on top of his usual workload.

His non-stop approach has proved controversial, with critics accusing him of running France single-handedly to the detriment of democratic institutions. But he claims that the country needs a dynamic reformer at the helm and says he was not elected “to watch trains go past”. The danger now — even if the malaise proves as minor as officials claim — is that he may have to slow the breakneck speed which has become his trademark, and that the French discover they have “un homme” rather than “un sûrhomme” — a superman — at their head.

Commentators have questioned whether he would be able to carry out his planned duties this week, which involve naming at least three under-secretaries to the Government, travelling to Normandy and presiding over a Cabinet meeting on Wednesday. After the meeting, he is due to spend three weeks on holiday at his wife’s second home on the French Riviera.

The announcement of his collapse came as a surprise to French media unused to such transparency from heads of state. When Georges Pompidou fell ill with Waldenström’s macroglobulinemia — a form of cancer — news outlets said that he was suffering from flu. It was only when he died in 1974 that the population discovered the truth. François Mitterrand hid his prostate cancer for 11 years after his election in 1981.

President Sarkozy promised a new policy of openness during his election campaign in 2007. But later that year he underwent an operation on a throat abscess at Val-de-Grâce hospital which was kept secret for months.

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