The annoying thing about being sick -- well, there are a lot of annoying things. One thing in particular is the sheer variability of it. Sometimes you feel better than others. For a few minutes maybe you have some energy to work with; then it vanishes, and you collapse into an unpleasant clammy sleep. It's hard to make plans. Hard to be sure, even when you do feel better, that it's going to last. All of which said, it's important not to exaggerate: things could be a lot worse for me.
It's just damned frustrating.