If you think that worrying will make you more healthy, then by all means worry away. I’ve never found it to help a great deal, though. If it sharpens your focus in some way to take precautions that you would otherwise ignore – and if they seem wise in your cold, analytical view – then in that narrow sense worry might be indicated, and helpful. But again, if you’re a sentient adult who normally makes rational decisions (or if you believe that you do in all honesty, because sometimes rationality itself can be spoofed, and as Feynman says “first you must stop trying to fool people, and you’re the easiest one of all to fool”), then you probably won’t get a lot of benefit from worry, and it can detract a great deal from living in the moment (or paradoxically, prevent you from making plans for the future which may involve “acceptable risk” – worry can turn your considerations of “acceptable risk” into “certain calamity”, and dampen your enthusiasm for living a more enjoyable life). So my advice is to not worry, and to be happy instead. I think a wise man once said that, but I can’t be certain. In any case, if the lab results indicated a higher-than-normal white blood cell count, as the nurse indicates, then they simply want to get a better baseline reading when you’re feeling up to par. You may still be infected with a deadly disease (I don’t want to sugar-coat this, after all), but at least it will be a better baseline reading. And I’m sure that I’m kidding about the deadly disease. They just want a baseline from “the normal you” with no transient illness or upset condition.