Asurvey has just revealed that the average Brit spends the equivalent of 315 days of their life with a hangover - now there's a sobering thought!

Macmillan Cancer Support carried out the survey to launch their Go Sober for October fundraising campaign, which involves getting people to sponsor you not to drink a drop of booze for the month.

But what's going on as we're hanging after a heavy night?

Heads, ears and eyes

You wake up with a banging headache, dry mouth and your tongue seems to have grown a carpet. You also have blood-shot eyes and find noise intolerable

"All due to dehydration," says Mel Wakeman, a senior lecturer from Birmingham City University's Faculty of Health. "Alcohol is a diuretic [makes us pee a lot], so our body essentially becomes dry."

Very heavy boozing can also lead to deafness.

Mind

Details of the night before are hazy. You also feel depressed and full of dread. "Alcohol affects brain cells and stops them from storing information in our memory bank, particularly short-term memories," says Wakeman.

Booze can also affect memory in the long term. A study published in the American Journal of Geriatric Psychiatry assessed the mental abilities of almost 7,000 middle-aged people and found those with a history of drinking problems had a more than doubled risk of severe memory impairment later.

As for our moods, alcohol's a depressant, affecting neurotransmitters - brain chemicals - and possibly resulting in us feeling angry, teary, depressed and anxious for days and weeks afterwards.

Alertness

You can't stop yawning and have difficulty concentrating

All that brain chemistry disruption may play a part in why you're not feeling sharp, but another big factor is poor sleep.

Christina Merryfield, lead dietician at Bupa Cromwell Hospital, says: "If you have a lot to drink, you may need to get up in the night to go to the toilet. Secondly, a deep sleep helps the body to restore itself, but alcohol can interfere with the first stage of sleeping. This disruption may also contribute to making you feel drained when you wake up."

Gut and stomach

You've got diarrhoea and might be throwing up or craving carbs

"Alcohol can raise stomach acids, which causes you to feel nauseous," says Merryfield.

Feeling sick can also be due to a high concentration of alcohol in the stomach and bloodstream.

Stomach acid changes can also cause heartburn, and may be why you've got the runs - though some people may also be sensitive to sugars in certain drinks.

As for those cravings for stodge and sugar, that's largely linked to low blood sugar. "Many alcoholic drinks are rich in carbohydrates, making our blood sugars surge, followed by a crash," says Wakeman. "We get the munchies or feel hungry in response."

Arms and legs

OK, so you were dancing a lot but the booze you were glugging will probably have played a part in your aching arms and legs.

Again, dehydration has a lot to answer for. "Loss of fluid affects the blood flow through all of our body tissues," says Wakeman.

And what about the stuff you're not immediately aware of?

l Liver damage: It's the liver's job to break down alcohol, but this can damage it. Symptoms include weight loss, jaundice, feeling sick and vomiting blood, but often damage will be silent "until around 75 per cent of the liver is damaged", notes Wakeman.

l Cancer risk: Alcohol's a risk factor for cancers, including liver, breast and bowel. It's estimated alcohol causes 4 per cent of UK cancers, 12,500, each year.

l High blood pressure: A major factor in life-threatening conditions such as heart disease and stroke, high blood pressure is often referred to as the "silent killer". Research has found that alcohol can increase blood pressure, both during a boozy night, and in the long term.

l Weakened immunity: "Alcohol can reduce the absorption of nutrients, so if you drink over the recommended amount on a regular basis, in time, a reduction in nutrients, along with damage to your liver and other organs, will reduce your ability to fight off infections," says Merryfield.

Be a Sober Hero and sign up for Macmillan Cancer Support's Go Sober for October challenge, being sponsored to give up booze from October 1-31. For more information, visit gosober.org.uk