It has been christened Blue Monday, and one mental health professional believes the bad weather, failing New Year's resolutions, feeling unmotivated and wanting to take action can all contribute to feeling low.
In 2005 Dr Cliff Arnall, formerly of Cardiff University, created a formula that brings together all the factors of a really depressing day - and he believes it happens on the third Monday of January.
And while some remain sceptical about whether Blue Monday actually exists or instead if it is being used as a canny marketing ploy, the Public Health Agency (PHA) has welcomed the chance to draw attention to mental health issues.
Seamus Mullan said January can be a challenging time for those returning to work after the Christmas period, but he added the PHA does have some tips to help prevent people from feeling down.
"Be active, get plenty of exercise," he said.
"Also be connected, talk to friends and family. Research shows that people who are in touch with friends and family more than once a week are less likely to be prone to depression or mental health illness."
They are also encouraging people to look out for friends and family who may need help.
"If people are really in crisis or concerned about their own mental health or that of others, the Lifeline confidential support line is available for people 24 hours a day, seven days a week," said Mr Mullan.
The PHA said this is now an ideal time to think about the things that make you happy, and to do something that makes you laugh.
So while the snow is still falling outside and the days remain long and dark, remember there is an upside - it is just six months until the happiest day of the year.