Wish people would stop saying flu floors you. As with anything it can effect everyone to a different degree. Sitting in a chair is not beyond the realms of possibility when you have the flu. The difference between a cold and the flu is pretty evident.
Flu is horrible, but I felt better watching tv at my desk in a chair and upright than lying down in bed with nothing to do but focus on aches and pains. Cough less and feel better upright than lying down as well.
Got it 3, maybe 4 weeks ago, felt fine in the morning, mid afternoon my throat was painful and I felt odd, went to sleep for 6 hours, woke up feeling god awful. Aching everywhere, throat felt almost closed up and incredibly painful to swallow, stinking headache. I got up, drank a little, had a bit of milk and a couple codeine + ibuprofen pills and felt marginally better. I plonked myself down in my chair and barely moved for 3 days, bathroom and fridge for cold drinks was as much as I wanted to do, attempting to sleep when tired enough for that to overcome everything else.
Woke up four days later, fever gone, aches 90% gone, feeling 90% better but also woke up feeling utterly and completely drained of energy. Coughed badly for two weeks, with coughing frequently inducing migraines(which I get when not ill) and felt completely exhausted the entire time. It left me feeling wiped out for basically the entire month.
Cold = slight temp, cough, sore throat, bit of a headache(because I'm prone to them more than anything), no real energy loss, no real trouble sleeping, no real need to sit around all day feeling like I was dying.
To sum up
Well enough to fap, cold. Can't fap... flu.