Redfred is incorrect about being able to be sick as many days as you like, but only a certan number of occassions per year. There is also a limit for flying crew of 10 days per year. (This includes the day you called up sick, even if it was a day off. So people have taken to giving no notice, and calling on the day of report. Not a good thing for crewing purposes, but this is what the rules make us do.)
im not wrong aslong as you dont have more than 2 occasions in a certain period of time you will be ok so a week here then 2 weeks there wont hurt unless its in a short space of time
also all shift workers lose shift pay if they are sick