Student or Learner
Is it "you are so sick, as a result you felt terrible" or "you should be sick in order to feel terrible"? Is it purpose or result?
ex)Yet hundreds of times a day we engage in everything from stray negativity to outright trains of thought that, over time, beat us up. Tha physical equivalent might be something like taking tiny poison pills that wear down your body. Imagine being not so sick that you couldn't function, but sick enough so that you felt terrible most of the time. In a way, that's how many of us live our lives on an emotional level. We surely function, yet we are stressed and miserable....
Feeling terrible is the result of being sick/ill.
The wording in the original is fine.
"I'm not so sick that I can't come to work, but I'm sick enough that I don't want to eat anything".