I learned this from one of my former superiors whom I admire. That if you’re not feeling well, feverish maybe, or simply not feeling well, and there are important tasks to do (which never diminish anyway), please, get that one day of rest. Take advantage of that sick leave and give yourself a break. Stay home and just rest. Drink lots of water. Eat well. Just rest. Your employer is not going to pay for your hospital bills anyway in case you report for work, be devoted to your job but only end up getting more sick for a long number of days. It’s not worth it.