Hillary Clinton was escorted from the September 11 commemorations at Ground Zero supported by a woman in a navy dress.

And, as the woman held on to her arm, appearing to take her pulse, the Tennessee branch of the Republican Party tweeted that the woman could be Mrs Clinton’s “undercover nurse”.

The concept caught fire on social media – despite the fact that it would not be remarkable for presidential candidates to have medical professionals on standby, and that it would be strange for her medical professionals to be dressed in a nurse's outfit.

Others even repeated wild, widely-ridiculed claims that she was suffering from early Parkinson's disease.

Mrs Clinton's doctor, Lisa Bardack, confirmed in a statement on Sunday evening that she had diagnosed Mrs Clinton with pneumonia on Friday, and advised her to rest. Dr Bardack stated that Sunday's episode occurred due to the combination of that diagnosis, dehydration and overheating.

But critics of the 68-year-old used the latest health scare to paint a picture of a woman too elderly and infirm to be president.

In 2009 she fractured her elbow and needed surgery, and in 2012 she fell and suffered a blood clot on the brain. Conspiracy theorists have suggested that this has left her with permanent mental issues.