Doctor: What Clinton's stumble tells us

That the Clinton campaign didn't release the diagnosis of pneumonia on Friday is symptomatic of its own problems.

The video clearly shows someone who's on the verge of fainting (medically, the term for such temporary loss of consciousness is syncope, or if the person doesn't actually pass out, it's pre-syncope). Yet Clinton's spokesman Nick Merrill said the candidate "felt overheated so departed to go to her daughter's apartment." "Feeling overheated" lacks the important detail that she couldn't hold herself up on her own as she got into the waiting vehicle.

But while the Clinton campaign once again managed to foster the perception that they're preoccupied by information over-control, we shouldn't let their odd behavior get in the way of interpreting the facts we have now.

The "differential diagnosis" list, or range of potential problems to consider, when someone faints is huge. But about half the time doctors don't need to do any special testing to figure out the problem. A simple physical exam, or even the history alone (or story) of the event settles the diagnosis in such cases.

Hillary Clinton's episode Sunday looks like one of those straightforward cases, and it's not surprising Bardack is confident in the factors at play.

First, Clinton experienced warning symptoms, namely the sensation of overheating (and perhaps other symptoms her team hasn't supplied), which prompted her to decide to leave an outdoor event in the summer sun after she'd attended for about 90 minutes. Each of these facts is crucial.

The most important job doctors face when evaluating a brief fainting spell is figuring out whether the heart is involved. Did the heart skip into a bad rhythm, one that wasn't able to get enough blood supply to the brain? If that happens, in most cases, the event is sudden and with no warning, unlike in Clinton's case. In such situations the person also rebounds fairly suddenly. They don't need a rest and recovery period to gradually return to baseline like Clinton did.

Clinton's gradual onset of symptoms also come in the context of her attending an outdoor event for an extended period that involved a lot of standing. This is key medical history that points to a blood pressure drop, and the most common cause of that is a so-called vasovagal episode.

In typical vasovagal syncope, there's less blood in the upper body when you're standing because it's pooling in the lower body, and maybe you're dehydrated to boot. Your heart tries to forcefully contract to make up for the lack of sufficient blood in its chambers, so much so that it overstimulates itself into activating an arm of the nervous system that's normally responsible for bringing down the heart rate and blood pressure (the parasympathetic nervous system, which connects to the heart through the vagus nerve - the "vagal" in vasovagal).

Prolonged standing is just one of many common causes of vasovagal syncope, another is overheating, which also dilates blood vessels and drops blood pressure. While the New York air itself wasn't particularly hot Sunday morning (lower 80s), the air temperature doesn't dictate your surface temperature in the sun, which can still send plenty of heat into your body and clothing (especially if dark like Clinton's outfit). Anyone who's enjoyed Southern California's wonderful weather has experienced this phenomenon.

Beyond the pneumonia, I also suspect that Clinton's allergies, which her doctor described in her medical attestation last year and which we've all heard about thanks to the candidate's periodic coughing fits, played a role. Coughing, whether due to pneumonia or allergies, can itself kick off a reflexive surge in the parasympathetic nervous system that drops the blood pressure and causes you to faint.

In short, if Clinton came into an emergency room with this history, most ER doctors wouldn't see the need to refer her for advanced testing.

But of significant concern to me is that Clinton told reporters Tuesday that she "just upped my antihistamine load to try to break through" her latest allergy exacerbation.

Antihistamines need to be used in moderation. The potential side effects are broad, they're a brute weapon in the battle against allergies because they interplay with the nervous system. The drug class is well known to play a role in fainting spells, and if Clinton just increased her dose this week, that's a factor her doctor should consider in her future allergy management.

But what about Clinton's history of a concussion and a blood clot in her brain in late 2012 (cerebral venous sinus thrombosis)? This piece of medical history is of the greatest interest to Clinton's health conspiracy theorists, but it's the least likely factor in her near fainting spell Sunday.

Because of prior blood clots in her legs, and the one that occurred in a brain blood vessel, her doctor decided to start her on the blood thinner warfarin, and she's taking that chronically. Video shows Clinton emerging from her daughter's apartment having recovered fairly quickly. If another cerebral venous thrombosis or other brain circulation issue had occurred, she wouldn't be back in business so quickly.

Respiratory infections that progress to the lung, i.e. pneumonia, are exceedingly common, particularly in older adults like Clinton. They are among the normal medical events in anyone's life, and both pneumonia and a fainting spell both will feature strongly in the average lifespan. That said, bugs causing pneumonia are more serious than others, and may point to other underlying conditions.

I would like to see the Federal Election Commission regularly convene panels of independent physicians to review the chief executive candidate's medical records in fine detail. Such a panel would then issue a believable third-party check (more important for some candidates' doctors than others).

Such a review could benefit the candidates as well as the nation: Sometimes it helps to have more than one medical set of eyes. There are successful companies dedicated to the concept of second and third opinions, and our chief executive deserves to benefit from that level of care.

You needn't be the picture of health to serve as President of the United States, but even if you are, you're never above an infection or a fainting spell.