Aaargh. I feel terrible. This is worse than my New Year's Day hangover. I've got aches and pains all over. Is this the dreaded 'flu they say is rampaging across the country, or have I just caught a cold? It could be 'flu. This is the season for it. There's a strain called H3N2 Sydney - after the Australian capital where it was first identified - which has been laying thousands low in the Midlands in the past few weeks.

Isn't 'flu just another name for a bad cold? Oh no. The two get bandied about interchangeably by skivers looking for an extra day off after Christmas, but although viruses cause both, influenza is a potential killer, while a cold is nothing a hanky and some hot lemon won't sort out.

Thanks for the sympathy. But how do you tell the difference? Above all, says Professor John Oxford, virologist from the London Hospital Medical College, flu makes you feel so bad you want to stay in bed - in fact, you really cannot bear to do anything more than hide under the duvet. You have aches and pains - maybe stabbing pains - all over your body. You've got a headache and maybe a cough and you may develop a fever, with a temperature of up to 104 degrees, or chills which make you shake, sweating, a sore throat, fatigue - oh, and a blocked nose.

So one of those 'flu-strength' cold cures isn't going to sort me out? Correct. This is a virus in your respiratory tract that you've picked up from somebody coughing or sneezing near you, which doesn't linger in your nose and throat the way a cold virus does. It moves down your breathing tube and into the beginning of the lung itself, if you're unlucky.

Then what? Most healthy people will fight it off, but in the vulnerable, the virus may attack the cells that line the air sacs, giving the bacteria that normally live in the throat a chance to get in and do some damage. That's why doctors prescribe antibiotics for the beginnings of bronchial pneumonia.

So I'm going to die? No - you're just going to feel like death for five days or so, being a relatively healthy individual. But it is not unusual for 3,000 to 4,000 people in the UK to die every year, and in a bad year the toll can reach 25,000.

Who is vulnerable? Elderly people and those with chronic medical conditions principally. Anyone over 65, resident in a nursing home, suffering from chronic heart or lung disease, children with asthma, women over three months pregnant and others at risk should have been vaccinated by now.

I thought vaccines didn't work? Too many different strains of 'flu about? Yes and no. Each year experts hold a pow-wow at the World Health Organisation and decide which three strains are going to hit us next winter. They got it right this year - Sydney is in the vaccine. But they make up the stocks in the summer (since they use eight million chicken's eggs it takes a while), so they can't be sure of getting it right every time.

Shall I rush off and get a jab now? Pointless, since you're infected already. Better just sweat it out. And besides, stocks will be low. Vaccination time is October. Just make a note in your diary for next year.

But come on, I want some help. What can I do? Feed a 'flu and starve pneumonia, perhaps? Drink plenty and eat normally if you can. Stay in bed and rest. Take some paracetamol for the muscle aches and pains. But see the doctor if you don't get over it within days.

Why haven't we got a cure if it's a killer, then? It is on the cards. Two pharmaceutical companies are racing to get some promising new drugs called neuraminadase on the market. They seem to be able to stop the virus reproducing in the body. They could be available this time next year.

Future cures are all very well, but what about our present epidemic? Wrong. It is not an epidemic until 400 people per 100,000 population are ill. This is normal for the 'flu season - around 100 per 100,000. But it looks worse in some patches where the concentration is higher. North and central England have it worst.

Aren't we due for a massive outbreak? Probably. There have been three pandemics, in 1918, 1957 and 1968. It's been a long time since the last, so every country in the world is now on standby for the Big One.

What will happen if it comes along? There probably won't be any vaccine, because we'll be hit by a strain we haven't guessed at in time, or else there will be limited supplies. So decisions will have to be made as to who is a priority - doctors and nurses first, or nobody will get any treatment. Retired nurses may be drafted in, emergency clinics will be set up and plans made for dealing with the large numbers dying.

I don't want to hear any more. I'm going to bed.

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