She's not faking. But in the spirit of "never let a good crisis go to waste," I think the pneumonia diagnosis, which I don't believe given her history, is a perfect cover for whatever more serious chronic illness she has.
Pneumonia can be cured, but perhaps not fast enough for her to be in the debates, which gives her a good excuse to miss them, without it reflecting on her general health issues.
If she cant debate, she cant run a country. Period.