Yeah this honestly sounds like some grade A conspiracy crap.
Even if Hillary does have Parkinsons and they're covering it up, it's the 21st century. People can and do live productive lives despite suffering from Parkinsons. It's treatable to an extent and many people can manage the symptoms and live relatively normal lives, so it wouldn't exactly disqualify someone from being president. Certainly no more than suferring from Alzeimer's, which we have anecdotal evidence makes you one of the most popular presidents of your era.
People have also diagnosed Donald Trump with various mental disorders from watching videos of him. No credible evidence for that either. Like Ink said, an old lady falling down after standing in the heat for 90 minutes (while running a presidential campaign so probably not sleeping enough) isn't exactly a mindblowing revelation.
Edit: JUST DISCOVERED, video evidence that Trump has a degenerative nervous system disorder characterised by having
absolutely no rhythm