At his rallies he talks very forcefully and for long periods, coming across convincingly. He holds numerous press conferences, fielding open questions while she went almost a year without a single press conference. Her focus seems to be more on fund raising events, with friendly controlled environment.
She already has a pot of money. Maybe she lacks confidence that she will be able to stay the grueling course and could have to saturate the airwaves with ads to supplement her limited appearances.
Then came the video clip.
Feeling sick at the 9/11 memorial event. she shakes her press corp and tries to sneak out an hour early. The change in schedule catches out her staff and she has to wait a short while for the vehicle pick up. Just long enough for an observer to capture images of her stumbling toward the vehicle before being saved by her secret service from falling to the ground. I have lost count of the times I have seen this video clip played during the day on many networks. Not a good visual Hillary!
In her typical difficulty with the truth, she declares she overheated, but two days after the diagnosis has to admit it is pneumonia. This brings renewed demands for both candidates to disclose medical records.
Following this collapse she retreats to her daughters apartment nearby, instead of to the hospital. The m/o here is reminiscent of her actions when Benghazi was under attack. i.e. risk the consequences rather than draw attention to the problem. Or maybe she was concerned a visit to the hospital could bring to public attention a direful revelation.
I have personally experienced pneumonia three years ago, during which I was given a 50/50 chance of surviving. It is not something you want to be carrying during the final weeks of a Presidential campaign and not two weeks before going up against Trump on the debate stage watched by probably the biggest T.V. audience ever.