A raging sore throat and headache, soaring temperature, and horrible tiredness you just can't shake - if it's not the self-inflicted 'symptoms' of a stinking hangover, it may well be that you've caught glandular fever.

The dreaded illness mostly affects teenagers and young adults, although you can still catch it later in life, if your body hasn't built up a hardy immunity against it.

This highly-infectious virus can leave you utterly exhausted and bedridden - and as is the cruel nature of life, it's particularly rife during the festive period, when people begin locking lips under the mistletoe, as it's passed from person to person through saliva (hence why it's often referred to as the 'kissing disease').

Here, GP and Healthspan medical director, Dr Sarah Brewer, explains more about glandular fever and how to avoid it this Christmas - and what to do if you are unlucky enough to catch it.

What actually causes glandular fever?

Also known as infectious mononucleosis, or 'mono', glandular fever is caused by the Epstein-Barr virus (EBV). Once a person catches it, it's generally thought that the virus remains in their system for life, though it usually does not cause further illness.

However, it can leave people very poorly for months - and it's also linked with Chronic Fatigue Syndrome (ME), which may sometimes, it's believed, be triggered by the virus.

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The main reason you feel terrible when you catch glandular fever is because your immune system goes into overdrive to fight off the virus. "Many of the worst symptoms associated with the fever are due to the body overreacting to the infection and attempting to flush it out as fast as possible," notes Dr Brewer.

So you get it from kissing?

Yes, you can get it from locking lips, but that's not the only way it's spread. "UEBV is passed on in saliva, so it can also travel by coughing, spluttering, sneezing and by sharing toothbrushes," says Dr Brewer. "Someone who has recently had glandular fever can remain infectious for several months, but only half the people who catch the virus develop symptoms."

What are the symptoms?

Anyone who has suffered with this nasty virus will tell you that it isn't pleasant. Glandular fever mainly produces flu-like symptoms and can be quite severe, with aching, fatigue, a high temperature, severe sore throat that isn't getting better as quickly as you'd normally expect, and swollen glands, especially in the neck. Thankfully, for most people, the worst symptoms usually resolve within three weeks, although sometimes complications can occur.

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"The spleen and liver can also become enlarged and tender," says Dr Brewer. If you develop difficulty breathing or swallowing fluids, or severe abdominal pain, she advises that you go to A&E or phone for an ambulance.

How is glandular fever treated?

Like many illnesses, there is no cure for glandular fever, so you'll have to wait out your painful throat with the old-fashioned combination of bed rest, fluids and painkillers. "A short course of steroids are sometimes prescribed if tonsils are very swollen and affect breathing," says Dr Brewer, although these will be prescribed by your doctor after an assessment of the symptoms.

If you're someone that's always on-the-go, make sure you take things down a notch. "It's important to take things easy for several months after glandular fever, to allow the immune system time to recover," says Dr Brewer.

Children and teens will need some time off school, while adults should take some time off work to get a few days of undisturbed rest - and then gently ease yourself back into your normal schedule.

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"During convalescence, it is common to feel tired, depressed and lacking in energy for six months or more," says Dr Brewer. She recommends trying a magnesium supplement (Healthspan's Magnesium, £9.45 for 90 tablets, also contains B vitamins), which may also help to reduce your fatigue.

If your appetite is reduced, you can take a multivitamin and mineral supplement to help support your immune system while the worst of the symptoms pass.

"Avoid kissing and sharing utensils for at least two months after your symptoms begin," advises Dr Brewer. It's also a good to be vigilant with your hand hygiene - frequent washing with antibacterial soap is important, especially after coughing or sneezing - and clean any areas in your house that you've been around, to avoid spreading the virus.

Finally, it might not be the news you want to hear just before Christmas, but going teetotal will also help the recovery process along. "During this time, the liver is not functioning properly," says Dr Brewer, "so avoid drinking alcohol where possible."