Bosses across the UK are set to contend with more worker absenteeism due to a fake illness on 6 February than on any other day, research suggests.
A quarter of those surveyed had pretended to be ill when calling work
And Liverpool seems to be the UK sickie capital. Workers take 13 days off sick each year compared to three in London.
Lifestyle expert Prof Cary Cooper, who aided the study, said early February was "gloomy" and "many people are still feeling the post-Christmas blues".
Some 4,000 workers were surveyed by TV channel Sky Travel for the study.
Nearly half of those questioned said they will take at least one unauthorised day off sick this year, either to catch up on sleep, extend a weekend break, recover from a hangover, or go shopping.
And one in four of those surveyed had pretended to be ill when they called in sick by coughing or spluttering down the phone.
More than half carried on the pretence when they returned to work.
Barbara Gibbon, General Manager, Sky Travel, said: "It is clear that an increasing number of employees feel completely justified in taking a cheeky day off sick.
"February 6 seems to be popular for a myriad of reasons, not least the fact that many people will be finding out that they are still in debt despite the fact that they have just been paid."
Researchers found that widespread dissatisfaction with the number of official holidays, coupled with a need to recharge batteries after the initial post-Christmas shock of being back in the office, made February the most common time for absenteeism.
Meanwhile, hugely increased workloads also lead to more genuine illness.
The prospect of having to wait for a Bank Holiday and a reluctance to take annual leave persuaded people to stay at home, the study showed.
A TUC spokesman said: "The truth is that sickness absence is going down.
"Employees are more likely to struggle into work when they are too ill than let colleagues down by throwing a bogus sickie."
He also stressed that many people are genuinely ill early in the year.
"With February a top month for colds and flu, the worry is that people with genuine illness will now have to struggle into work and infect their colleagues to avoid suspicion of cheating," he said.
The study also highlighted a number of trends.
For example, it seems that workers in the North of England are more likely to pull a sickie.
And women said they believed they could get away with having twice as many sick days than their male counterparts.