It isn't possible to perform at your normal levels while you're sick.
A cough, the flu, coronavirus; You'll have to postpone meetings and deadlines for a couple of days, rest in bed until your body fights whatever is making you feel like crap, and catch up with work whenever you feel better.
That's why we need to let some buffer time into our schedules; you don't know if you'll be able to perform at 100% tomorrow.