With a significant number of top physicians expressing concern that the American people aren't being told the truth about Hillary Clinton's health, the Democratic Party nominee's personal doctor is declaring she is fit to return to the campaign trail.

The letter from Dr. Lisa Bardack was distributed by the campaign Wednesday after a video of Clinton apparently collapsing as aides helped her enter her limousine during a 9/11 memorial Sunday confirmed suspicions over the past several months that she is seriously ill.

Concerns about reported fainting spells, stumbles, blood clots, uncontrollable coughing and a "serious" concussion that took "months," however, are being attributed to "dehydration," "flu" or "pneumonia" by her campaign.

Bardack works in the internal medicine section at CareMount Medical in Mount Kisco, New York.

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"My overall impression," she wrote," is that Mrs. Clinton has remained healthy and has not developed new medical conditions this year other than a sinus and ear infection and her recently diagnosed pneumonia. She is recovering well with antibiotics and rest. She continues to remain healthy and fit to serve as president of the United States."

But her two-page letter addressed none of the issues captured on video, including her violent head-jerking in one episode and her blank stare and loss of focus in another.

Dr. Jane Orient, executive director of the Association of American Physicians and Surgeons, told WND the letter from Bardack "ignores all the pertinent questions."

"Maybe she has pneumonia, but the timing is perfect for explaining a fall we weren't supposed to see and which could have been caused by same neurological damage that caused previous falls," she said.

Dr. Lee Hieb, author of "Surviving the Medical Meltdown: Your Guide to Living Through the Disaster of Obamacare," took no time in expressing alarm.

"From a distance, without formal evaluation there are still three things I know for sure regarding Hillary Clinton's medical condition: 1) She has a neurological disorder; 2) pneumonia did not cause the episode on 9/11; and 3) she and her staff have been lying to cover up the truth of her condition for months if not years."

She explained: "I practice orthopedics and am fellowship trained in spinal surgery. As such, I do quite a lot of neurological valuation in my clinic. And as an orthopedic surgeon, I take care of fractures in elderly people who fall. Now, everyone falls occasionally, and as we get older we fall a little more frequently. But even people with loss of sensation in their feet, people with weak muscles and people with chronic conditions like cancer don't fall that frequently. There are only two groups of people who fall a lot – raging alcoholics and people with neurological disorders. If Hillary were drinking herself into falling, she would not have been able to perform at her usual job/campaign. But, for over a year, she has fallen on camera and behind camera. We are told of heat stroke, dehydration and other reasons to justify multiple falling episodes. She has fallen and broken her elbow and fallen and hit her head hard enough apparently to cause bleeding.

"And let's look at how she is falling. After the 9/11 ceremony, she is seen 'collapsing' on the way to her vehicle. Now people who faint due to low blood pressure, sudden illness, heat stress, etc. slump limply. They are easy to support and care for. Not so Hillary's episode. Watch it yourself and you will see she is rigid and in spinal extension. After a few seconds of wrestling that abnormal posture her handlers are able to get her into the car."

Hieb said pneumonia "does not explain any of this."

"Her staff may have decided – because coughing is often associated with pneumonia – that they could get away with blaming her problems on that condition. But not so fast. Any doctor who has treated pneumonia can affirm that if you are sick enough to pass out, you are not going to recover in an hour to become a smiling, waving Hillary exiting her daughter's condo. And her cough is chronic. Are we really expected to believe her doctors couldn't make a diagnosis of pneumonia – if that's what it is – after months to years of cough? Like take an X-ray? Recently chronic cough has been shown to often be neurogenic in nature. It is associated with stroke and can be ameliorated with spinal cord modulating drugs such as gabapentin. So there is a more probable explanation to her cough."

She then brought all the evidence together.

"I knew she must have a neurological disorder but had dismissed Parkinson's because of her facial animation. Parkinson's is characterized by 'frozen' face – patients are without normal smiling, etc. But it was pointed out by other more astute clinicians that head bobbing and exaggerated eye and facial movement is seen in late treatment of Parkinson's patients on chronic levodopa – the classic medical intervention," she said.

"Parkinson's is a disease of group of diseases where patients have neurological symptoms due to loss of the neurotransmitter dopamine. It is characterized by rigidity, flat facial affect, swallowing and speech disorders, and inability to initiate motion. Parkinson's patients are notorious for falling during 'freeze' episodes because they cannot initiate movement to catch their balance. And they often fall hard because they cannot get their hands out to protect themselves (note Hillary's head trauma episode)."

There are other possibilities, such as Progressive Supranuclear Palsey, which attacks people in Clinton's age group and is similar to Parkinson's. But she believes Clinton's issues are neurological.

"What is absolutely clear to anyone willing to think is that Hillary's health issue has been covered up and the American public has been lied to. But all the queen's soldiers and all the queen's men are failing to make it through the end game. Hillary now has handlers who help unfreeze her by running up on stage and reassuring her and touching her to get her mobile again."

Hieb also noted Clinton is "being kept away from spontaneous crowds and questions which might trigger an event."

"Why not come clean? Because people with Parkinson's very frequently have dementia, cognitive deficits (reasoning problems), mood alterations and can have anger issues as well as the more obvious balance and motor problems. And when the 'dementia' label in any way attaches itself to Hillary, it is game over for her political future," she said.

"I do not wish her ill, and I hope she will avail herself of the latest thinking in the subject of Parkinson's and Parkinson-like disorders. If I were her, I'd go immediately to Florida for a visit with Dr. David Perlmutter, who for years has been really thinking outside the box with neurodegenerative diseases."

WND has assembled the Big List of doctors who have raised questions about Clinton's health, and two of them previously raised the issue of a possible diagnosis of Parkinson's.

A board certified internist cited by Powerline blogger Scott Johnson suggests the pneumonia is a symptom of something much worse: a stroke or possibly Parkinson's.

The physician wrote: "During my 19 years as a board certified internist I have taken care of many hundreds of patients with pneumonia. The story about Hillary Clinton being diagnosed with pneumonia raises a red flag as to the cause. It could simply have been a community acquired pneumonia, which means she contracted it as a healthy person living her usual life. This happens occasionally, even to healthy people. If this is the case the timing certainly is unfortunate for her given where we are in the election cycle though it doesn’t portend anything ominous."

However, the internist noted there is another "more worrisome possibility."

"I raise this second possibility because of Hillary’s history of neurological illnesses (blood clot in brain, concussion), hints raised on the Internet in Wikileaks documents and by others that she may have a neurological disease like Parkinson’s, and her by now well documented history of recurrent coughing fits. This second possibility is that she has an aspiration pneumonia.

"Aspiration pneumonia occurs when fluids and food particles that normally enter the esophagus instead enter the windpipe and lungs. It is commonly seen in neurological conditions like strokes and Parkinson's disease or similar diseases where the nerves to the swallowing mechanism are not working properly. This is especially worrisome because it is likely to recur given the underlying, usually incurable disease process and because it can be a life-threatening event," he said. "I consider aspiration pneumonia to be the more likely cause because it unifies all the pieces of disparate information that are available on Hillary's medical condition. A diagnosis of aspiration pneumonia raises profoundly troubling implications for her possible election as president."

Also, Dr. Ted Noel, at his blog VidZette, assembled a 16-minute video concluding the evidence suggests she has had Parkinson's and has known about it for several years.

"Everything … fits the theory," he said. "Video evidence is solid. [There's] strong evidence of having advanced Parkinson's disease."

And that, he contended, makes her "medically unfit" for the Oval Office.

See his explanation:

Clinton returned to the campaign trail on Thursday with a carefully scripted trip to North Carolina, even as polls showed Trump building a lead over her in battleground states.

The Democrat candidate's plunge in support may partly be explained by the fact many people don't believe her.

The Washington Times reported on Wednesday "half" of voters say Clinton "has given false information about her health."

The report cited the Morning Consult poll, which found only 29 percent "said Mrs. Clinton has given accurate information about her personal health to the public."

Former Secretary of State Colin Powell was told by a local political official, according to emails released this week, that Clinton was barely able to climb the steps to a podium to give a speech.

On Wednesday, when the Bardack letter was released, two physicians who comment on Fox News responded to questions on Sean Hannity's show.

Dr. David Samadi noted that after last weekend's collapse in New York, Clinton will need a medical team around her constantly.

"If it happens again, this would be a big problem for her," he said.

See the discussion:

As the latest health questions arose about Clinton, the London Daily Mail reported that in 1998, Clinton suffered a blood clot but told her staff she had a pulled muscle.

She was first lady at the time and "did not correct White House staffers when they assumed the problem with her right leg was due to over exercising."

WND's Big List of doctors who are raising questions about her health includes former presidential candidate Dr. Ben Carson, who said she should undergo tests and release the results.

Orient has said images of Clinton being helped up stairs and propped up, and videos showing odd, seizure-like head movements require an explanation to voters. The author of "Emerging Diseases: Protecting Your Family from Pandemics, Viral Threats, and Rogue Vaccines" noted the "vituperation and anger" she's faced for raising questions.

"I'm not making a diagnosis," she told WND. "(But) I can look at the video. You can look."

She said that for a medical professional to simply ignore the evidence would be "completely reckless." Meeting someone with these symptoms personally would require a, "How are you?" she said.

"These are not ridiculous questions."

Much of the evidence supporting questions being raised is in videos that are readily available:

One appears to show her losing her concentration while speaking.

She comes to a halt and stares at the audience.

See the video:

And a July 21 video posted on YouTube shows Clinton's head suddenly turning and shaking vigorously for several seconds.

Blogger Jim Hoft of the Gateway Pundit headlined it, "Wow!" Did Hillary Clinton Just Suffer a Seizure on Camera?"

"The poor woman is in worse shape than we thought," he wrote