Every year it's the same: when autumn arrives and the days grow shorter, something inside you switches off. You struggle to get up, you drag tiredness around all day, you take refuge in food and the urge to see people disappears. And when spring returns, almost without noticing, you become yourself again. If you recognise this, it may not be laziness or coincidence: it could be seasonal affective disorder.
Seasonal affective disorder (SAD) —also called seasonal depression— is a type of depression that comes and goes with the seasons, almost always in autumn and winter. In this article I'll explain what it is, why it happens, what symptoms it has and what you can do to get through the dark months more easily.
What seasonal affective disorder is
Seasonal affective disorder is a type of depression that follows a seasonal pattern: the symptoms start at roughly the same time each year and lift when the season changes. The American Psychological Association describes it as depressive episodes that appear and disappear with the seasons. In the diagnostic manuals it isn't a separate illness but a depression "with a seasonal pattern". The most common form, by far, is the one that arrives with the cold.
Why it happens: the role of light
The main cause of seasonal affective disorder is the lack of sunlight. When the days grow shorter, the internal clock —the circadian rhythm— gets out of sync, and substances that regulate sleep and mood, such as melatonin (which makes us sleepy) and serotonin (linked to wellbeing), fall out of balance. In some people, who are especially sensitive to these light changes, that imbalance is enough to trigger a depressive episode. So it isn't a matter of willpower: it's your body reacting very real to an environment with less sun.
Symptoms of seasonal affective disorder
The winter form has some very characteristic symptoms, often different from classic depression (where sleeping and eating little is more typical).
Signs that set it apart from a passing dip
- A lot of sleepiness and great difficulty getting up, even if you sleep many hours (hypersomnia).
- Constant tiredness and a sense of running on empty all day.
- Increased appetite, especially for sweets and carbs, with a tendency to gain weight.
- Sadness or emptiness most of the day and loss of interest in what you used to enjoy.
- Difficulty concentrating and a feeling of mental fog.
- The urge to withdraw, to shut yourself away at home and see no one.
Winter depression (and the lesser-known summer type)
When we talk about seasonal affective disorder we almost always picture the winter kind, which begins in autumn and improves in spring. But there's a much rarer variant, the summer type, in which symptoms appear with the heat and often look more like classic depression: insomnia, loss of appetite and restlessness. Whatever the season, what defines this disorder is its regularity: year after year, the same time of year brings you down.
Who it affects most
Seasonal affective disorder is more common in women and in younger adults, and it tends to appear more the further from the equator you live, because the differences in daylight hours between seasons are greater. There's also more risk if you've already had depression or other mood problems, or if there's a family history. Having some of these factors doesn't mean you'll get it, but it helps to stay aware.
How it affects daily life
Even though it lifts on its own when the season changes, while it lasts seasonal affective disorder takes a real toll. The mix of excessive sleep, tiredness and low mood makes it hard to perform at work or in your studies, pushes you to withdraw from people and leads you to drop activities and self-care you used to take for granted. The changes in sleep and appetite feed the distress, and the circle closes. If your sleep goes completely off track, it can help to look at these keys on sleep disorders too.
Seasonal affective disorder or post-holiday blues?
They're easy to confuse because both arrive when summer ends, but they aren't the same. The post-holiday blues is a brief adjustment to going back to routine: it lasts a few days or a couple of weeks and passes on its own. Seasonal affective disorder, by contrast, is deeper and more persistent, tied to the lack of light rather than to the return to work, and it repeats every year with the same pattern. If the "September dip" doesn't lift and gets worse as it grows dark earlier, it's worth paying attention.
What you can do to feel better
The good news is that there's a lot you can do about seasonal affective disorder, and that getting ahead of it before the cold sets in helps a great deal. It isn't about "just trying harder", but about giving your body what it's missing —above all light— and keeping up habits that protect you through the hard months.
Make the most of natural light
Since the lack of light is the root of the problem, actively seeking it out is the first remedy. Go outside every day, especially in the morning, even when it's cloudy; open the blinds first thing; sit near windows; and, if you can, take a walk when it's brightest. It doesn't have to be sunny: daylight outdoors is far more intense than indoor light and already has an effect on your internal clock.
Look after your routines and sleep
The circadian disruption is at the heart of seasonal affective disorder, so giving your day structure helps a lot. Try to get up and go to bed at regular times, even when your body begs you to stay in bed; avoid long naps; and watch what you eat, because carb cravings are common but leave you feeling even heavier. Stable hours are an anchor when everything invites you to let go.
Move and don't isolate yourself
When you have seasonal affective disorder, your body asks for the sofa and solitude, and that's exactly the opposite of what you need. Physical activity, even a short walk, lifts your mood and regulates sleep; and keeping in touch with people, even when you don't feel like it, stops the hole from getting deeper. It doesn't have to be perfect: small, steady gestures count for more than big resolutions that never happen.
Light therapy and other treatments
One of the best-evidenced treatments for winter seasonal affective disorder is light therapy: exposing yourself each morning, for a while, to an intense, specific artificial light that mimics sunlight. According to the US National Institute of Mental Health (NIMH), light, psychotherapy and, in some cases, medication are effective options that are often combined. Light therapy should always be done with the right guidance and, if you take medication or have other health conditions, after checking with a professional first.
When to seek professional help
Changing your habits is great, but there are times when you need support. Seek help if the sadness, tiredness or lack of motivation last for weeks, if your sleep or appetite go off track, if you can't function normally or if year after year winter becomes an uphill struggle. The UK National Health Service (NHS) recommends seeking help when the symptoms interfere with your day to day. And if thoughts of harming yourself appear, get help urgently by calling your local emergency number or a crisis line (in Spain, 024, the suicide helpline).
How therapy helps
In therapy we work on seasonal affective disorder in a practical way: understanding your pattern so you can get ahead of it, activating yourself little by little when everything invites you to stop, examining the thoughts that come with low mood and building routines of light, sleep and movement that carry you through the dark months. When needed, we coordinate the biological side with your doctor. I do this through therapy for depression and, if it suits you better, with online therapy, in English, Spanish or Catalan. If you notice your low mood becoming chronic outside the season, it can also help to rule out dysthymia.
If you've recognised yourself here, get in touch for a first assessment with no obligation. And hold on to this: seasonal affective disorder isn't weakness or laziness; it's a real response to the lack of light, and it can be prevented and treated so that winter stops being something you just have to survive.