Why do I feel guilty ringing in sick?

[MakeMineALarge1]

I am due in work tomorrow, I have a genuine reason for not going in, but I can't ring in, I feel guilty as I know they are short staffed and this will add to it.
Why do some people ring in at the drop of a hat for very small issues, yet when I have a genuine issue I don't.
I accept I am probably a bit of a martyr.

UPDATE

Went to a&e, had a dose of IV abx, had to return today for another dose, now on them for a week.

I should stop feeling guilty