At my current job, I’m constantly busy (sometimes overloaded) but rarely are there things going on that I and only I can handle and that must be done TODAY. Usually either one of my coworkers can cover or it can wait. We also get generous sick(can use up to 3 days at a time without dr. note), personal(for anything, preferably with notice) and vacation time(needs notice but we get a ton) which helps balance out the lower than industry standard salaries. The institutional culture encourages us all to use our leave as well, there aren’t unspoken penalties for it come review time.
Given this, I stay home if I think I might be contagious (see WhyNot’s great guide), if I need a day in bed to heal from something, or if I feel I’ll be working at less than 60% of my optimum efficiency due to pain, nausea or whatever. If I’m that inefficient I’m actually costing the org more in the long run because I’ll be dragging ass and letting stuff slide all week, so I may as well take the day and get better. Interestingly, I never (ever - like maybe once when I had mono at 16) get fevers. I think it’s just not in my immune arsenal, but also my body runs a few degrees colder than standard when I’m healthy. If I got them I’d use that as a gauge too. I have been known to take a mental health day or “sick of this darn place” day, but only once or twice a year and only if I know I’m not leaving anyone in the lurch by doing so. And really, those fall under the 60% efficiency rubric too, as I do it when I know I’ll just be distracted or depressed all day and not get much done anyhow.
How many days a year this translates to varies widely. The year of 2009 was a doozy for me, following a ton of personal upheaval I was basically sick all year with a rotating cycle of respiratory infections, plus I had a huge course of dental work done. This led to me missing at least a day each month, some of which I made up on weekends and such. Conversely, I think I’ve only been out sick one or two days so far in 2012. I have taken a day here and there for “sick of this place” but I was able to plan them a few days in advance and use legit personal time for them so no weasling needed.
At my last job, things were very different. We were scheduled down to the half hour most days, and calling in meant great difficulty for anyone else on shift. I was one of a few full time employees and the rest were students on tight schedules of their own so getting extra coverage simply didn’t happen. So, I took one sick day in the 2 years I worked that job. If I was sick I spent slack hours lying down under my desk and left early if I could, but dammit I was there! I miss that job a lot but not that aspect at all.