Hillary Clinton is facing new questions over whether she brought her personal doctor, Lisa Bardack, to the 9/11 memorial where she collapsed.

The Democratic candidate had a woman at her side throughout her time there - and as she was escorted away, the woman appeared to check Clinton's pulse.

She also held Clinton's hand in a way which it has been suggested may have been some sort of neurological test.

The woman was also seen whispering in Clinton's ear in a video taken of VIPs at the commemoration.

A series of Twitter users have questioned whether it is Dr Lisa Bardack, the physician who diagnosed her with pneumonia.

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Taking her pulse? Questions have been raised over whether the woman seen here on NBC footage of Clinton at the memorial was checking her vital signs and therefore medically trained

Holding her hand: A photograph of the immediate seconds after Clinton left the front row of the memorial shows the woman holding the candidate's hand

Diagnosis: Dr Lisa Bardack, who confirmed on Sunday that Clinton was diagnosed with pneumonia Friday. It has been suggested that she was at Clinton's side at the memorial

Present throughout: The woman was with Clinton as she arrived for Sunday's 9/11 commemoration ceremony. Clinton had been diagnosed with pneumonia on Friday but kept it secret

Close to the candidate: As Clinton made her way through the crowd, the woman was close by

Clinton-whisperer: As names beginning with the letter B were read out at the ceremony, the woman whispered at length in Clinton's ear

Front-row place: Clinton was beside New York senator Chuck Schumer (left) and in the same row as (from right) Chris Christie, the New Jersey governor; Donald Trump, her presidential rival, Rudolph Giliuani, New York mayor during 9/11; Bill de Blasio, the city's current mayor; and Michael Bloomberg, the mayor in between Giuliani and de Blasio

The presence of someone with medical training would raise concern that Clinton went to the event knowing her health was at risk.

She is already facing criticism for keeping her diagnosis with pneumonia two days earlier secret - and for her campaign taking hours to admit the truth.

The campaign's changing story on Sunday saw aides claim first that she was 'overheated' and then that she was suffering because of heat and humidity - on a day in New York which other people thought was a pleasant late summer morning.

Finally, at 5pm on Sunday, there was an admission that she had pneumonia, which the campaign said had been diagnosed by Dr Bardack.

CLINTON'S DOCTOR Lisa Bardack has been Hillary Clinton's 'long time' personal physician. Exactly how long is unknown, as the candidate has not published her full medical records. Dr Bardack, 52, works for CareMount Medical, a network of 400 physicians in New York State, where the Clinton have their home. A New York University medical graduate, she is the group's chair of internal medicine and usually works at its Mount Kisco campus, close to Chappaqua. Advertisement

Dr Bardack has been suggested to be to be the woman who was at Clinton's side as she was escorted away from the memorial.

The campaign has not commented on whether she is. DailyMail.com is also trying to contact Dr Bardack.

The dark-haired woman was accompanied by a Secret Service agent who is part of Clinton's regular security detail as she helped Clinton away from the memorial, and towards the van waiting for her.

On the way there, she held Clinton's hand in a gesture which has been suggested to be either taking her pulse, or a test for neurological damage.

The neurological test is one of a series administered to check that the brain is correctly instructing the body and has not suffered damage in some form.

The woman is not one of Clinton's well-known aides often seen at her side, including Huma Abedin, her closest assistant, and is not known to have been seen with Clinton before.

The woman appears to have stood directly behind Clinton and whispered at length in her ear, video footage of the memorial service itself also discloses.

Twitter is alight with rumors that someone is keeping tabs on Clinton's health at all times, and that the candidate may even be suffering neurological damage.

Supporting role: As Clinton collapsed getting into the Secret Service 'Scooby van', the woman was to her left holding her

Escort: The woman was directly beside Clinton as she was led away from the memorial, to the surprise of other people there

'Undercover': This photo appears to show a woman, described as an 'undercover nurse' checking Clinton's pulse prior to her collapse on Sunday, while Clinton clutches her heart

Rumors: Pictures apparently showing Clinton squeezing the woman's fingers also revived much derided rumors that Clinton is suffering from Parkinson's disease

Doctor who? Some Twitter users suggested the mystery woman was Clinton's doctor, Lisa Bardack, although this could not be confirmed.

Clinton collapsed outside her van during Sunday's 9/11 memorial service in New York and was rushed to her daughter's apartment.

Although the collapse was initially written off as 'overheating' by the Clinton camp, Dr Bardack, later confirmed that she had been diagnosed with pneumonia on Friday.

But photographs of Clinton being walked to the SUV appear to show her being tended to by a woman in a blue dress, whom many believe is a nurse.

A Twitter account titled 'Tennessee GOP' posted a picture of Clinton with her right hand on her heart and her left hand and wrist clasped by the woman.

'Undercover nurse checking Hillary's pulse?!' the tweet asked.

And a second picture, posted by Mathijs Koenraadt showed Clinton talking to the woman, apparently holding her fingers.

'#Hillary squeezing her nurse's fingers,' the user wrote. 'Clearly, she's disoriented. Final stages of Parkinson's disease?'

The woman in question was identified by some as Dr Bardack, but she could not be contacted for comment, and does not appear certain to be the woman.

The sentiments in both Tweets were echoed by numerous other users, under the hashtags #HillaryHealth and #ClintonCollapse.

Claims that Clinton has been suffering from Parkinson's disease have long circulated, although they have never been taken seriously outside of conspiracy theory groups.

Similar concerns also emerged about the presidential candidate having suffered brain or neurological damage as a result of her 2012 diagnoses of a blood clot in her brain, which came after she collapsed due to dehydration and suffered concussion.

She had also suffered two previous blood clots, in 1998 and 2009, as well as suffering a fractured elbow in 2009 after suffering a fall.

Clinton also collapsed in January 2005, reportedly due to a GI virus.