My thoughts as well. At first I thought that this "Hillary is sick" business was tin foil hat stuff. Once the WaPo and others started attacking Trump's mental health, and debunking Clinton's, it became obvious they were not only in a projection mode, but in one to either dilute of completely marginalize her problems.
Cook clearly knows what it's like to deal with someone in declining health when his mentor and friend, Steve Jobs, clearly started to decline in health after the first cancer diagnosis in 2003. As such, though Cook will not admit it publicly, if he sees that Hillary Clinton has serious health problems, he may not offer 100% support for her campaign, possibly out of fear she could become incapacitated (or worse!) well before Election Day.