[dTal]

>I do tend to be a bit suspicious of the one-day "under the weather" events.

If you don't normalize one-day "under the weather" events, you are trading them for multi-day "off sick" events.

Personal anecdata: I recall once at a job with a particularly easygoing boss I simply didn't feel up to my morning commute, for no easily definable reason. I rang in sick anyway and went back to sleep. I then proceeded to more or less sleep through the entire following 24 hours, until it was time to go to work again. Lo and behold I magically had the energy this time, and bounced into work. I then realized that I had been suffering from fatigue from the early stages of an infection which I had successfully fended off through rest - had I dragged myself into work, I most assuredly would not have been there the following day, and probably not the day after that either.