Teacher Sick Days

I'm having a sick day at home today, having fought with an incoming cold for all of the week. I find it really difficult to keep going with teaching when a head-cold hits.
I usually notice it first by how tired I feel at lunchtime. Then my throat starts to get croaky, and I have to work twice as hard to keep my class on task. I also find that I start messing up everyone's names! Before I know it, I'm feeling completely incompetent at my job and stressed out by the whole thing.
So why do we teachers do this to ourselves?
Sometimes, I think we feel that our program is too important to miss a day, and that no one but us can present the program the way we have designed it.
Sometimes we love the lessons we have prepared too much to hand them over to someone else. WE want to be there to see how they turn out!
Sometimes we feel that a day off will disrupt the class too much and they will riot, and be hard to refocus on our return.
Sometimes we have too much administrative stuff to get through, and don't feel we can afford to take the day off - too much to prepare (for interviews, reports, assessment, learning journeys etc).
What are your reasons for going to work when you are on death's door?