I was thinking of weight lifting too (anything would do, I did some pecs exercises at times with a huge Latin dictionary

). I never got pneumonia, but when I catch a cold, I know I still usually manage to go on with that, even if not lifting as much as I could when in good health, while cardio leaves me completely flat and winded out, as I don't have much stamina when sick. Now, as said, I have no idea of how exactly one feels after a pneumonia, so if this seems hard for you, don't do it