Are you sick or "sick"?

I read an article a few years ago about HR managers and their complaints about employees.  Survey said that when you call in sick, your manager doesn't believe you 75% of the time.  We had a three day weekend for MLK day at work this week, and today is the first day back.  A shocking number of people called in sick.  So, riddle me this: are they sick, or are they "sick"?