How many times have you been hung-over? I have no idea - which probably implies, and rightly so, that the figure's pretty high.

By the sounds of it, that's the case for most of us, as a survey's 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 basically involves getting people to sponsor you not to drink a drop of booze for the month of October.

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

HEAD, 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 Wakemen, 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. Headaches can be caused by this, as blood flow to the brain changes.

"Your eyes dry out, so there is less fluid to lubricate the eyeballs. And you generally become oversensitive to noise when your head hurts."

Very heavy boozing over prolonged periods can sometimes lead to long-term hearing problems. "Alcohol may also damage the sensitive parts of the inner ear that help us hear sounds, and can lead to deafness," Wakeman adds.

MIND

:: Details of the night before are hazy. You also feel down in the dumps, or even depressed and full of dread

It's not uncommon to experience some degree of memory loss, particularly after a very heavy drinking session. "Alcohol affects brain cells and stops them from storing information in our memory bank, i.e. stops us making memories, 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 this summer assessed the mental abilities of almost 7,000 middle-aged people across eight years, and found those with a history of drinking problems had a more than doubled risk of severe memory impairment further down the line.

As for our moods, while we may get a buzz and feel perkier after a couple of drinks, alcohol's actually a depressant, affecting neurotransmitters - brain chemicals - and possibly resulting in us feeling angry, teary and even depressed and anxious for days and weeks afterwards.

ALERTNESS

:: You can't stop yawning and have difficulty concentrating

When you're extremely hung-over, even getting from bed to sofa can feel like an achievement, and watching re-runs of your favourite comedy is the most your brain can handle. As above, all that brain chemistry disruption may play a part in why you're not feeling sharp, but another big factor is the poor night's sleep you've just had.

"Alcohol can disrupt sleep for a number of reasons," says Christina Merryfield, lead dietician at Bupa Cromwell Hospital. "Firstly, 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 affect the initial process needed for deep sleep by interfering with the first stage of sleeping, called 'rapid eye movement' [REM]. This disruption may also contribute to making you feel drained when you wake up.

"Finally, drinking also relaxes muscles, so although you can feel relaxed, you are more likely to snore loudly, causing yourself to wake up!"

GUT AND STOMACH

:: You've got diarrhoea and might be feeling queasy and throwing up, or completely ravenous and craving carbs

"Alcohol can upset your stomach by raising your stomach acids, which causes you to feel nauseous and unwell," says Merryfield. "This usually lasts 24 hours, but can be longer if you've drunk excessively."

Feeling - and being - sick can also be due to a high concentration of alcohol in your stomach and bloodstream; especially bad if you've been mixing your drinks. "It's our body's way of protecting itself - by making us feel rough, it's giving us some aversion therapy to stop us doing it again!"

Stomach acid changes can also cause heartburn, and may explain why you've got the runs - though some people, especially those with irritable bowel syndrome (IBS), may also be sensitive to the 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 upwards, followed by a downward crash as our body attempts to regulate our levels," says Wakemen. "We often get the munchies or feel hungry in response."

Drops in blood sugar are also what cause some people to feel shaky, weak and dizzy, Merryfield points out, which is why it's "important never to drink on an empty stomach".

ARMS AND LEGS

:: Limbs feel heavy, tired and sluggish

OK, so you were giving Jacko a run for his money on the dance floor until the early hours, and that might have something to do with why your arms and legs are aching so much, but the booze you were glugging will probably have played a part too.

Yet again, dehydration has a lot to answer for. "Loss of fluid in the body affects the blood flow through all of our body tissues," Wakemen points out, so this includes all your muscles and connective joint tissues. Low blood sugar might also be a factor, as you'll generally have less energy all over.

AND WHAT ABOUT THE STUFF YOU'RE NOT IMMEDIATELY AWARE OF?

When we drink too much, too often, damage can accumulate over time, and may not cause immediately obvious symptoms...

:: Liver damage

It's the liver's job to break down alcohol, but this can damage it. The liver can regenerate itself - but only up to a certain point, and too much booze over long periods of time leads to liver disease. Recently, experts have warned that this is happening in increasing numbers of younger patients across the UK.

Symptoms include weight loss, jaundice (yellowing of skin and eyes), feeling sick and vomiting blood, but often damage will be silent "until around 75% of the liver is damaged", notes Wakemen. "At which point, it won't be able to perform its jobs for the body and you are well down the road to permanent liver damage."

:: Cancer risk

Research has found that alcohol's a risk factor for a number of cancers, including liver, breast and bowel cancer, with people who drink within the recommended guidelines generally having less chance of developing the disease. It's estimated that, every year, alcohol causes some 4% of UK cancer cases, which equates to around 12,500.

:: High blood pressure

A major factor in life-threatening conditions like heart disease and stroke, high blood pressure is often referred to as the 'silent killer' - because people usually don't know they have it until it's picked up by tests, as it rarely causes obvious symptoms. Research has found that alcohol can increase blood pressure, both in the short-term during a boozy night, and in the long-term for those who often drink heavily.

:: Weakened immunity

Ever wondered why you seem to feel run-down all the time, and keep getting colds when you've been burning the candle at both ends? Disrupted sleep, due to boozing, can affect the body's ability to fight off infections, as can dips in nutrition. "Alcohol can reduce the absorption of some 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 and you'll be more prone to illness," 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