All schtick aside, and my personal dislike for Clinton aside as well - there are several reasons why this is a serious issue.
1. She is 68 years old. Whether you agree or not - her health is an issue (so is Trump's by the way). The job of president, by all accounts is both physically and mentally demanding - almost 24 hours a day. Testing whether a person can withstand the rigors of the job is as important as whether they know about Aleppo.
2. The Trump campaign has been hitting her hard on health issues going back to the primaries, and lately it seems as though the Trump surrogates have been engaged in a strong whisper campaign about Clinton's health. Until yesterday those whispers were met with derision - now it raises questions. From the outside, it looks to me, like the Trump campaign got some inside intel - prior to Friday - that Clinton is in poor health - so they have been laying the groundwork waiting on an episode like this for the seed to take root - knowing it was a matter of when, not if.
3. The optics of the "episode" are not good. In the era of 24-hour news and social media coverage - this was more than simply passing out from heat exhaustion. Ask Ray Rice about the power of video.
4. The trustworthy issues continue to haunt Clinton - I am not sure if we have the whole truth on this episode, and I bet I am not alone. The story went from feeling unwell from heat exhaustion, to fainting from heat exhaustion, to total news blackout, to she was diagnosed with pneumonia on Friday. The video was an unexpected wrinkle - since the media had been banned from leaving the media area of the ceremony. Once the video started to go viral, the story changed, and then the campaign went into blackout mode, then we get a fresh story. As with most Clinton stories - the story only changes as more facts become known. Even in the doctor's note - they are still trying to spin the health issue - the first sentence talks about her having a seasonal allergy cough - when we now know (or think we know) she was diagnosed with pneumonia - not seasonal allergies.
Even if you are the most staunch Hillary supporter, this should give you pause, and want to ask some fundamental questions around whether she is healthy enough to carry out one of the most demanding jobs in the world. Because, if she is not healthy, then we should really be doing a lot more vetting of Tim Kaine - who may be a fine candidate, but if that is who we are electing, then we should know a lot more about him than we currently know....