I have experienced something similar after I've been ill. For example, day 1 and 2 I'm just doing my work and don't feel ill yet, then day 3 I get ill and have

I have experienced something similar after I've been ill. For example, day 1 and 2 I'm just doing my work and don't feel ill yet, then day 3 I get ill and have to stay home from work. Afterwards I notice that my work from day 1 and 2 is way below average and can more or less be discarded, while I did not notice this at the time.