Today is Blue Monday, but here are 10 tips to stay cheerful.
Over the past three years, researchers analysed more than 2million tweets posted by Britons in January looking for negative language and phrases indicating a drop in mood.
They found that today, there will be nearly five times the average number of tweets relating to guilt, as people abandon their promises to pursue a healthier lifestyle.
Here's our advice on how to stay cheerful:
1 - Have a good breakfast, fuel your mind and body for the day ahead.
2 - Be nice to people you meet. Chances are, they'll be nice back.
3 - Booked a holiday this year? If not, start thinking about where you would like to go. If you're already booked up, then envisage being on that beach!
4 - It's not too late to make those new year resolutions. If you're not happy about something, make a change.
5 - Look ahead to the weekend. Make plans to see friends.
6 - Get those headphones on and listen to your favourite music.
7 - Not happy in your job? Have a scout around for a new career in your lunch break. Don't fear change.
8 - Treat yourself today and buy a film to watch tonight, give yourself something to look forward to.
9 - Don't clock watch. Time goes much slower when you focus on the time. Keep yourself busy and your first day back at work will be over before you know it!
10 - Negativity breeds. Surround yourself with positive people and smile.