It seems that civil servants in the UK took, on average, two weeks off work as 'sick leave' last year. Curiously the start day for such 'sick leave' was most often a Monday. Roughly a third of staff took no time off at all, and a further third took somewhere between one and five days off work a year each as 'sick leave'. So the remaining one third were taking much more than two weeks each.
In my working career of a little over twenty years I don't think I can have had to take more than five or ten days in all throughout that whole period. Luckily I enjoyed (and enjoy) pretty good health, but nor was there any particular pressure not to take time off when genuinely unwell. Personally I always felt it my duty to take time off if I was unwell with something even mildly infectious (a cold, for example) or, obviously, more infectious (e.g. conjunctivitis, which I had on one occasion). I also occasionally had to insist that staff working for me take time off for similar reasons.
I suspect civil servants behave somewhat differently because the tapxpayer has no choice whether to continue to fund the 'businesses' these people work for. And apart from cases of gross negligence or misconduct their employment is pretty secure. And if they waken up on a Monday not in the mood (for whatever reason) to go to work what can anybody do about it? Probably very little.