I agree with you about bein' silly to have a written note from a doctor, if they require you to do so. But, if you want to keep your job - then, it would be a wise to get a written note from a doctor to prove that you are really sick....then, maybe your boss can let you go home to prevent spreadin' your sick to others at worksite. 
My bf still have to get a written note from his doctor, if he gets sick... just to avoid losin' his points.
Hope you get well sooner ! 
