I used to work 12 hour shifts, 6 'til 6, 4 days then 4 days off, then 4 nights and 4 days off, of course there was overtime as well, after a night shift I wouldn't go to bed straight away, I would try and stay awake, after all, when we work days we don't go to bed as soon as we get in, looking back on it I don't think it helped that much, my body clock was always all over the place.