But, 'being jolly' often means attending a stream of pre-Christmas festivities. It can turn into a month of parties - corporate parties, the office party, friend's parties, neighbour's parties - that never seem to stop.
Christmas jollities are great for boosting office morale, getting to know colleagues better, or even just having a good time at the company's expense. According to a recent survey of 200 professionals carried out by Scoot, the consumer transaction service, 80% of those polled think Christmas parties are good for office morale.
However, all this partying means that December can also turn into the month of hangovers. It becomes very easy to slip into a cycle of drinking, being hungover and then drinking some more the following evening. After all, you want to join in the party mood and everyone else will probably be in a similar state the next morning, so why not you too?
Problems arise when hangovers start affecting your performance at work. A lot of bosses will tolerate employees being a bit ropey on the odd occasion, particularly the day after an office do. But if you regularly turn up throughout December nursing a storming hangover, it can look like you don't take your job seriously.
Diane Sanclair, employee relations adviser at the Institute of Personnel and Development, warns employees should be careful not to overstep the mark. "You must remember your employer won't turn into Santa Claus even though it's Christmas time," she says. "Some employers are happy to turn a blind eye to some relaxing of your work environment, but you have to be sensible. You have got to be shrewd about what will cause disruption to the business. Nothing should change in your behaviour or performance."
Being sensible means making sure you are in a fit state to do a good day's work. This is particularly the case for anyone who is in a position of responsibility or has dealings with other people.
Say you work in support or have several important meetings to attend. It's not going to reflect well on you if you turn up looking dog-eared, reeking of booze and clutching a packet of hangover remedies.
You also have to remember that you are not just representing yourself - employers will be concerned that your behaviour will reflect badly on the department or company.
If you know you are going to have a heavy session on a particular evening, it's advisable to make sure there aren't any business-critical decisions to make the following morning.
Be wise about what you will be able to achieve and make plans. A real luxury is to take the following morning off, or even the whole day. It is certainly better than calling in sick and leaving people in the lurch.
Anyone who has any doubts about the importance of maintaining a professional attitude during this month should remember what Sanclair has to say: "A fair dismissal can still take place on Christmas Eve."
Nutritionist Natalie Savona has given her five top tips to beat a debilitating hangover: