Just a heads-up. In the late '80s I had changed jobs and almost from day one I had a persistent dry cough pretty much whenever I tried to talk. It didn't seem to get worse, but it didn't go away. I might have been a bit weakened, and maybe a bit tired from all the coughing (a great ab workout, eh?), but I was able to get by. After about 2-3 weeks or so I had enough and went to see a doctor. She diagnosed me with ambulatory pneumonia ("walking pneumonia" in lay parlance), which the doctor said I probably contracted when someone coughed on me. It's still pneumonia, but sufficiently mild and not debilitating enough for people to normally seek immediate treatment. She prescribed antibiotics and after a day or two, I started to feel better, well before the prescription ran out. Of course, I was only 30 at the time, so maybe my relative youth had something to do with a very quick recovery.
I say this for two reasons. First, it exists, because I had it. Second, when I read about Clinton's persistent cough, I was toying with the idea of e-mailing them through their website about what she night have had, based on my own personal experience. But I figured she was already being well looked after, and that it was probably something else.