I had real flu the week that the SARS flu worries started - having been in a conference most of the week with lots of people who had flown in from HK and the far east where there were lots of cases at the time.
I can remember realising I was poorly during the day but dosing up on paracetamol and neurofen to stave it off thinking it was just going to be a cold (and because I'd paid lots of money to be there). Walking towards the tube I saw a taxi and staggered into it because I couldn't face the tube and just didn't care about the cost, got home to my flat and collapsed on my bed,, that was it.
DP (as he was then) came home several hours later and found me in the exact same position, with a temp of 105 and apparently spent most of the next day sponging me to keep me cool, trying to get me to sip drinks and moving me every so often as I didn't have enough energy to roll over.
He didn't bother to get the doctor to come as he'd spoken to friends that were docs that had just said to keep on with the paracetamol and neurofen - and because he thought the flat was too messy 
to get a doc to come.
I had a temp at about 104 for the next 2 weeks and needed to recuperate for a good 3 months before getting back to anywhere near normal (had recently been made redundant so no pressures to be back at work without being ready, a mixed blessing). For most of that time you could have stuck a million pounds an inch away from my hand to be mine if I touched it - I just couldn't move, it hurt so much and beyond that I was so zonked I wouldn't have cared. Never been ill like that before (or again fingers crossed!)
Several weeks later I was reading an article about SARS and realised my symptoms fitted exactly - including the thing that the article highlighted (highlit?) as the difference between SARS and flu - but by then it was too late to find out what I'd had. Just know it was incredibly horrible and I'd never want to go through it again - and as other posters have said, get very annoyed when people say they have flu when actually they just have a nasty cold or virus - if they really did have flu they wouldn't have the energy to mention it for at least a month!