It's always after I recover from unwellness that it becomes clear to me how sick I was. I've been having more headaches/migraines - I had one overnight that faded this afternoon. 
Although I could barely hold a thought in my head, I was stumbling around forcing myself to "work", since it "had to be done", because surrendering and doing something as radical as lying down because of a "mere headache" was a "waste of time". I wasn't really "sick".
Then when the blinding brainstorm fades, it becomes apparent how much of a waste of time trying to push through really was. My "work" was painfully and poorly done, and done poorly at an immense energetic cost, when, once feeling better, it could all be done faster with less effort.
Somehow I always manage to forget that when I'm not sick, I have energy and feel like doing things (they go together!). Instead, it's like I believe that if I give in, once, to not feeling well, I'll never again have the drive to get out of bed!