Sad is one thing - but SAD is quite another, and tends to hit many of us in the Northern Hemisphere during the winter months. Seasonal Affective Disorder is characterised by a significant drop in mood, lack of energy, sadness and sleepiness during the colder months.
Scientists have now discovered that it;'s triggered by a lack of daylight, with the eye failing to send effective 'wake up' messages to the brain, due to low light levels. Currently, it's estimated that SAD affects around 3 in 100 people in the UK.
"Many of us may experience a lack of energy, low mood and change in sleeping patterns during the winter – especially after the clocks change. If these changes interfere with your everyday life you may have seasonal affective disorder," explains Fatmata Kamara, Mental Health Nurse Adviser at Bupa UK.
"SAD is often confused with periods of low mood or energy that many experience solely during the winter months – also known as ‘winter blues’", she explains, "but SAD is linked to reduced hours of sunlight in the shorter and darker winter months. This can affect your body’s internal clock, disrupting your usual sleep pattern.
"Reduced sunlight has been linked to a drop in serotonin levels (a hormone that stabilises mood and wellbeing) and an increase in melatonin (a hormone which regulates sleep cycles). Changes to these hormones can also trigger feelings of depression."
What are the symptoms?
"Symptoms of SAD are similar to other forms of depression, explains Kamara. "You may feel your overall wellbeing and mood is low and you lose interest in your usual activities. You may also find yourself lacking energy, struggling to sleep or a loss of appetite.
"Some people who suffer from SAD also experience physical symptoms such as headaches, heart palpitations and aches and pains."
Watch: Fighting seasonal depression as cold-weather months are upon us
What to do if you feel SAD
Enjoy natural sunlight during the day
"If the lack of daylight hours are affecting your mood, try to make the most of them and get outside when you can. Even on a cloudy day, getting outside will help your body to get the light it’s craving," says Kamara.
That's because SAD is not so much about vitamin D which we only get from sunshine, but daylight, regardless of whether it's sunny or not.
"Whether it’s a morning or lunchtime walk, wrap up warm and get outside in the fresh air to help boost your mood."
Work in a bright environment
"If you work indoors, whether from home or in the office, make an effort to let in as much sunlight into your working environment as you can. Open any curtains or blinds and sit by a window," says Kamara.
You can also invest in a SAD lamp, which replicates daylight. An hour or two a day in front of it can make a significant difference to mood.
"These lights which mimic the sun, are thought to boost levels of serotonin and melanin," she explains.
"Evidence around light-therapy is still not 100% conclusive, but it does look as though it can deliver positive short-term effects. This means it could be a helpful way to banish the winter blues until the days start getting longer."
The good news is that most sunlamps contain UV filters, meaning they’re not harmful in the same way that sunlight can be.
You can help to regulate mood by choosing a healthy diet. "A balanced diet helps to look after your physical and your mental health," Kamara says. "Your body is likely to be craving sugary foods so, try to balance your diet with foods such as, pasta, oats, cereals, nuts and seeds which help to release energy slowly.
"It’s important to make sure you’re getting all the proper nutrients and vitamins and foods rich in vitamin D and omega-3, such as oily fish, can help to improve mood."
Taking fish oil, iron tablets and a multivitamin may help, too.
David Brudö, CEO and co-founder of mental wellbeing and self-development platform, Remente, says, "Even if it might seem impossible to get outdoors to exercise when it’s cold and rainy, a regular exercise routine can make you feel significantly better, as exercising produces endorphins, leaving us feeling happier, and improving things such as quality of sleep.
"If a run outside is too much, then why not book in some classes at the gym, or even exercise from the comfort of home?"
The joy of Youtube and fitness apps means there's always an exercise class or routine on tap. Try yoga for mental strength and energy, or a HIIT routine for a fast burst of endorphins.
Sort your sleep
Going to bed and getting up at the same time each day can help you stay balanced, says Brudö.
"Practising sleep hygiene will leave you feeling happier and make you more productive on a day-to-day basis, so try to go to bed and wake up at the same time that you normally would throughout the year," he says.
"If you have a hard time unwinding, try a short meditation session before bed."
If none of the above suggestions help, however, it's important that you see your GP and get a proper diagnosis and a treatment plan.
Watch: Seasonal Depression in kids: Does your child have seasonal affective disorder?