i am lucky that my boss and co-workers in OUR department have no problem with us using our sick days as personal days or, "mental health days" as we call them.

i'll use them for a ski day, or tack on to the end of a vacation week - and if for some reason i get sick with no time left i'd just take an unpaid day.

luckily i haven't been really sick in a few years, had the flu for a couple days a few years back - but if i am working to hard (or biking to much) and feel myself running down a bit i'll make sure i drink tea, relax, get a good long night's rest and i'm fine. - and i know bike commuting and lifting weights helps my immune system kick butt.