Q: I find myself losing focus and even nodding off at my desk around 4 p.m. What’s going on and how can I prevent that? — Alica R., Rochester, Minnesota A: You’re not alone. A survey conducted by OnePoll found that 21% of folks say they deal with an afternoon slump — usually around three o’clock — and for some reason, Tuesdays are the worst. (Maybe back-to-work Mondays are just too exhausting.) But there are a few solid reasons that it happens and some easy solutions. First, cortisol levels fluctuate during the course of the day and in the mid- or late afternoon, they can dip, bringing down…