While many of us may catch a case of the winter blues as the days get shorter, an estimated 10 million adults in the US and 2 million in the UK live with seasonal affective disorder.

This mental health condition, also known as seasonal depression, lasts around four to five months on average. “The appropriately named SAD, or seasonal affective disorder, is considered a type of depression characterised by its seasonal nature,” Jeff Temple, a professor at University of Texas Medical Branch and a licensed psychologist, tells HuffPost.

Unsurprisingly, people living farther north with less sunlight and earlier sunsets are more likely to experience SAD, likely due to the lack of sunlight and much shorter days. However, that doesn’t mean people in warmer, sunnier climates aren’t affected. While seasonal depression is much more common during the winter months, some people may experience seasonal depression during summer or during the colder season because of the fewer daylight hours. Women experience it more frequently than men.

A common misconception is that SAD is less serious than major depressive disorder because it doesn’t last all year round. However, people with this mental health condition explained to HuffPost that the symptoms of SAD are very real, and can even be debilitating.

Here’s what they want you to know:

Like those with major depressive disorder, people with SAD may experience a lack of motivation and a loss of interest in day-to-day activities.

“I have had SAD for about 12 years, but I didn’t recognize the pattern or be diagnosed until about five years ago,” Claire, an optometrist, tells HuffPost. (Claire, along with some others in this story, asked to keep her last name private so she could freely talk about her mental health condition.) “I am typically an early riser and consider myself a productive person. However, when SAD hits, I struggle to do even the smallest daily chores like doing the dishes or making dinner.”

Similarly, Rebecca, a grad student, says that she has a “difficult time keeping up with [her] self-care and workout routine during the winter months,” and finds it nearly impossible to “function at full capacity.”

Moreover, staying socially and emotionally connected to loved ones can require much more effort when coping with seasonal depression.

“The most prominent SAD symptoms I experience are loneliness and apathy. I tend to become quite numb in the winter months, and feel emotionally separated from the people around me,” says Vera, a freelance illustrator. “During regular depressive episodes, I may be able to ‘mask’ for most basic social interactions, whereas in winter seasons it’s not even an option. I’m too wiped out to even show up or pretend.”

SAD and sleep disturbances go hand in hand. Chloé Perrin, a bartender, has found that her symptoms of seasonal depression often manifest as constant exhaustion, leading to hypersomnia. Simply put, hypersomnia is characterised by recurring episodes of sleepiness during the day, difficulty waking up in the morning, and feeling tired despite oversleeping.

“My family used to joke that every winter I’d hibernate, whereas my sleep is otherwise normal-to-low the rest of the year and during other episodes,” she says.

Bella Sutter, a dancer with seasonal depression, explains that “getting out of bed feels impossible and my mornings normally start late.”

“I feel as if I would be better off hibernating through the winter because seasonal depression makes me feel like I’m half asleep anyway,” she adds.

Not only does seasonal depression impact sleep, but this mental health condition can have a negative impact on a person’s eating habits. Researchers have found a marked correlation between SAD and higher rates of disordered eating, including behaviours such as binging, purging and restricting food intake.

For Anna Samanamú, a high school paraprofessional and graphic designer, symptoms of SAD began when she was a teenager. “My appetite becomes affected [with SAD], and I would prefer to sleep rather than eat,” she says. “Unfortunately, that led me to have issues such as anaemia and Vitamin D deficiency.”

According to Temple, “seasonal affective disorder has a bi-directional relationship with other mood disorders like depression and bipolar disorder — meaning that people with one form are much more likely to develop or worsen the other.” Notably, SAD affects up to 20% of people with major depressive disorder, and 25% of people with bipolar disorder.

Rhiannon Bellia, who works in social services, has found that seasonal depression tends to exacerbate symptoms of other mental health conditions.

“My OCD gets a lot worse in the winter, it’s harder for me to focus and gauge time with my ADHD. With having autism, it’s also a bit harder for me to regulate sensory overwhelm,” Bellia says.

Temple explains that if symptoms such as losing interest in activities or feeling sad last “longer than a couple of weeks or [start] to interfere with your work, family, or relationships, then that’s a good sign that you may need some extra help.”

Fortunately, light therapy and cognitive behavioural therapy are proven to be effective treatments for people with SAD. The most beneficial at-home light therapy boxes provide light at 10,000 lux.

SAD is not simply feeling a little gloomy when the sun goes down; it is a serious mental health condition that can greatly impact every aspect of someone’s life.

“Please be kind to everyone who struggles with seasonal depression,” Samanamú says. “We are not lazy — sometimes there is just a disconnect from our minds and bodies. Many of us just need to take a little bit of time to become whole once again.”

• Mind, open Monday to Friday, 9am-6pm on 0300 123 3393.
• Samaritans offers a listening service which is open 24 hours a day, on 116 123 (UK and ROI – this number is FREE to call and will not appear on your phone bill).
• CALM (the Campaign Against Living Miserably) offer a helpline open 5pm-midnight, 365 days a year, on 0800 58 58 58, and a webchat service.
• The Mix is a free support service for people under 25. Call 0808 808 4994 or email help@themix.org.uk
• Rethink Mental Illness offers practical help through its advice line which can be reached on 0808 801 0525 (Monday to Friday 10am-4pm). More info can be found on rethink.org.