The half sickness

I threatened to call in sick to work today. (glad I didn't in one sense- I was bombarded for once) But I would've felt guilty. Why on earth would I feel guilty for not going to work? Well, I've come down the half sickness. Maybe you've heard of it or even worse experienced it. I've got a list of symptoms: stuffy nose, watery eyes, phlegm in my lungs/throat, an only occasional nasty cough and my head is a little cloudy at times. But I don't feel bad.
Why can't I just be sick or not sick? I hate the half-sick.