I know we have a good number of former teachers amongst us, and I'll bet you all staggered in when you felt like death because you knew a colleague would lose that precious free period to cover for you.
When I worked in the Inland Revenue, I felt able to telephone my line manager if I really felt ill, but as I had my own office and my work would simply wait for me to get back it was not such an issue.
I would think that the crucial difference is between people who have interesting jobs where they are in control of their own work, and people who have boring, repetitive jobs with no control.