I think that there is little doubt that Clinton is physically ill; to what degree is unknown. The coughing could be a nasty virus that's not going away anytime soon and she could have a weakened immune systems because of the medications that she is on. About five years ago, I had a sore throat, lost my voice twice, and I still have issues with sinuses and a tickle in my throat and and now am on my second earache with fluid build up this year. Everything else healthwise has checked out fine -- not a whole lot they can do with viruses but let them run their course.
As for her episodes of unusual behavior, teetering, falling, needing help standing and sitting ... that's much more concerning.