I am a Manager of a Nursing Home and when we are short staffed I try my best not to make the staff I am calling feel guilty. It is very hard though, but I think it is also down to personality too - some staff just say no and that is the end of that , but others start giving me reasons why they cant, and sound really guilty!. I try my best not to sound disappointed on the phone so they dont feel awful, but it is difficult!
However I do envy them at times being able to say No as when we have a trained nurse call in sick and they cant get anyone else - Being the Manager I have no choice (I know it is my job and thats what I get paid for), but when I have done a 10 hour shift and 2 hours later get called to come in and do a 12 hour night shift it can seriously make me cry!
However I digress!!
I understand how you feel - I didnt feel well the other night about midnight and thought "shall I call in sick or not". By 1am I didnt feel much better and was due in work for 7am and working until 8pm. I decided that I felt so guilty I would go in, so I did. But by 7am I felt much better, and then I kept thinking what if I had called in and now I feel so much better!!!!!!!!!!!!!!!!!!!!!!!
You are human and no-one can blame you for saying No and wanting a day for yourself! I think if you dont say No occassionally, then perhaps they would expect you to say yes all the time and then you would feel more obliged and more guilty!!