Christmas: 'tis the season to be completely and utterly knackered. Knackered and jolly, maybe. But knackered all the same. By the time you have negotiated the merry-go-round of non-stop parties, competitive eating and out-of-control boozing, sprawling comatose on the sofa after Christmas dinner looms like a dim light at the end of a foggy, congested tunnel. And that is before anyone has mentioned the bits that are meant to be hard work: the frantic shopping, cooking, decorating, finishing things off in the office.

So, how to get a moment to yourself? "You need to be ruthless and not be worried about what other people think about you," says Mike George, author of 1001 Ways to Relax. "We worry that people think we're avoiding them, so we go out and see them or stay out talking to them when we would rather be at home."

It is not only at Christmas that finding time to wind down - rather than leg it about competitively doing "relaxing" things - can be difficult. By the time you have fitted in the gym, your evening course, drinks with friends and trips to the cinema, theatre and galleries (must not fall behind on culture, of course), there is not much space in the diary for anything else. "We do lots of things for appearances' sake and the fear of losing approval of others, if that's what others are doing," George says. "If we don't go to the party, we think we might miss out, or our friends might think less of us for not going."

Except, of course, that everyone else is just praying for that night when they can swap their heels for a pair of kicked-in slippers, and sit on the sofa with the cat. Which is why being upfront about your reasons for refusing an invitation might go down better than you would think. "When you decline, be really honest about needing to take time for yourself," says George. "Explain that you've been out every night this week and you need an evening off. Or, if all else fails, there's always the phantom tummy bug - sometimes you just need to pull a sickie from your social life."

Thankfully, with many offices all but shutting down over Christmas and new year, there is no need to pull out the lame excuses at work. In fact, says Amanda Griffiths, professor of occupational health psychology at the University of Nottingham, going to work is good for your health. Recent research shows that being employed is beneficial physically and mentally. But we do need to take sensible breaks to relax. "In many ways we have become more aware of taking time off and you hear people talking about work-life balance a lot more now. People are becoming aware that it is important to try to achieve that balance."

So how to know when it is time to take a few days off for yourself? "Sometimes you just feel very tired," says Griffiths. "Maybe your quality of sleep isn't good, or if you are stressed you tend not to look after yourself very well - you stop eating properly or finding time for exercise. People also tend to smoke more or to use alcohol to help them relax, or neglect their family and friends because they are absorbed in work."

In the long term, ignoring these stress signals can lead to problems such as depression or anxiety. "A lot of people get themselves into quite a pickle before they realise what is going on," Griffiths says.

Building regular relaxation into your life can help you stay focused on balancing your time. Whether you need to book an afternoon for physical activity, such as pottering round the garden or the golf course, or just for sitting in front of the telly on some freshly plumped cushions does not matter. The key is to do something that completely clears stressful thoughts from your mind. And does not put new ones (like why you always have to do all the cleaning in this house, or why the laundry mountain never decreases) in there. Schedule in a time to trudge through the chores to keep them separate from your down time.

Relaxation is not a competitive sport - and, just because a bit of sitting about is not going to help you notch up your daily footsteps/minutes of activity/latest athletic diktat, or clean the fridge and mop the floor, does not mean it should be sniffed at. Particularly if you can fit in a quick snooze while you are at it. "Naps are very beneficial," says Professor Jim Horne, author of Sleep Faring - A Journey Through the Science of Sleep, and director of the sleep research centre at Loughborough University. "We are probably meant to have two sleeps a day; a long one at night and a shorter one in the afternoon. You should try for less than 20 minutes - otherwise you will reach deep sleep - but a 15 minute nap can be really quite refreshing without affecting nigh-time sleep."

Even better, all that sitting around not doing much is helping your body. For functions such as cell division in your skin, for example, your body needs to be at rest. Not sleep, just rest. "I think of sleep as by the brain for the brain," says Horne. "I argue that most body functions from the neck downwards can carry on quite normally without sleep as long as you do get rest."

Physical problems that tend to be associated with sleep deprivation (such as getting lots of coughs and colds, or more serious metabolic problems) are not actually to do with your lack of zeds, Horne says, although they might coincide with a period of lack of sleep. But instead of looking at no sleep as the cause of your problems, he suggests seeing it as a symptom of something else (such as a period of stress) that might be causing other problems.

But that is not to say you can ease off on the sleep. Your body might not fall to bits without it, but you brain will start to complain quite a lot. So how much is enough? "The average for a healthy adult is about seven hours a night," says Horne. "That's just counting the sleep itself, not the bit before when you're turning off the light or deciding when to get up in the morning."

Yikes. My average hours are looking a bit on the short side, which is why so many of us try to fill up on weekend sleep before returning to work and social duties. "You can't bank sleep, but what you can do is clear your sleep debt," says Horne. "You don't need to make up all the hours you've missed out on - try for about a half or a third of what you've lost."

Just do not try doing it all at once. A sleep of about 10 hours is what you are aiming for. "Your body clock doesn't like you having a long sleep. If you sleep for, say, 12 hours you're going to wake feeling a bit yucky - like you have jet lag," Horne says. It's worth getting up the stairs early before a long sleep too; there is some truth in the early to bed, early to rise maxim, thanks to that body clock desperately trying to make you wake up in the morning. Try to move your going-to-bed time, rather than your waking-up time.

And if you are still a bit frazzled? Take some deep breaths and think of doing some yoga - particularly the relaxation "corpse" pose that finishes a session. "It just puts everything back into a calm state," says Natasha Ahmad, a yoga teacher at the Life Centre in London. "If you've been doing handstands with children, for instance, they can be very high, very hyperactive afterwards. The posture puts them back on an even keel; it makes you feel at one with yourself."

Hopefully, you will reach the New Year with a spring in your step and rid of the shadows under your eyes. Now all you need to do is keep to your rest manifesto - make a resolution and actually stick to it. In 2007, I will make more time for, well, nothing. It has a nice ring to it, don't you think?