I was a manager for a retail store in the past. You have "sick" days but you don't really have sick days...if you understand what I'm saying.
One time I was so sick that I could hardly stand because I had so little energy from the fever. I still worked the entire day even though most of it involved sitting in a chair.
I've never called in sick for a real job although I did call in some during college when I had a student job.