I'm an otherwise pretty healthy person who gets knocked out by anything respiratory. My entire life, ever since I was a kid, if I get a cold, the flu, anything, it's going to be weeks to months of feeling terrible. I always hated how casual everyone around me was with their illness, like oh, it's just a cold, yeah, well that cold is going to have me unable to sleep for the next 2 weeks and feeling generally awful for at least the next 2 after that, so please wash your hands after you sneeze on them. Twice now I've had the flu and taken over 4 months to recover and stop feeling like my lungs were filling with fluid every time I did any type of exercise.