Sunday the Clocks Go Back and the Evenings Go Dark: Why Your Mood May Dip, and What the NHS Says Helps

Short answer: seasonal affective disorder (SAD) is a form of depression that arrives each autumn or winter and lifts in spring. The NHS lists the symptoms of seasonal affective disorder as a persistent low mood, loss of pleasure or interest in everyday things, irritability, feelings of despair, guilt and worthlessness, sleeping longer than normal and struggling to get up in the morning, feeling lethargic and sleepy during the day, difficulty concentrating, and an increased appetite, often with cravings for carbohydrate-heavy foods and weight gain. If you recognise this pattern in yourself and find it difficult to cope, see your GP: treatments range from daylight and exercise to talking therapies, light therapy and antidepressant medication.

At 2am this Sunday, 25 October 2026, the clocks go back to 1am and Britain leaves British Summer Time for Greenwich Mean Time. The date is fixed by the last-Sunday-in-October rule, and this year it is the earliest date the rule allows. The change itself takes a minute, but its effect on daily life is immediate: in London, sunset shifts from about 5.48pm on Saturday to about 4.46pm on Sunday. Suddenly the commute home happens in darkness, and it will stay that way for months.

Most people notice the change and adapt within days. But for a significant minority, the shrinking daylight brings something heavier than inconvenience. If your mood slides downhill every autumn as the evenings darken, and climbs back each spring, this guide explains what the NHS says about seasonal affective disorder: the symptoms to watch for, how it is diagnosed, and the treatments that can help.

This piece is the mood companion to our earlier article on what the extra hour does to your body when the clocks go back, which covered the population-level evidence on sleep, anxiety and heart-disease events around the clock change. This article is about feelings rather than physiology: the low mood, the heaviness, the sense that the dark evenings are doing something to your head. Both pieces belong to the same Sunday; the science piece explains the clock, and this one explains the cloud.

What seasonal affective disorder actually is

Seasonal affective disorder, usually shortened to SAD, is a type of depression that follows the seasons. The NHS describes it plainly: its symptoms are similar to those of normal depression, but they occur repetitively at a particular time of year. They usually start in the autumn or winter and improve in the spring.

The NHS is also clear that SAD affects people very differently. Some people find the condition a bit irritating, while for others it can be severe and have a significant impact on their day-to-day life. A small number of people experience the mirror image: symptoms in phases separated by unusually upbeat, energetic periods, although that pattern is far less common.

It helps to be precise about one thing. SAD is not a separate diagnosis with its own entry in the diagnostic manual. Clinicians treat it as major depression with a seasonal pattern: the same illness, on a timetable. That distinction matters, because it means the condition is taken as seriously as any other form of depression, and the treatments that work for depression are the ones doctors reach for here too.

What are the symptoms of seasonal affective disorder?

Because SAD is depression on a seasonal timetable, the symptom list starts with the signs of depression itself. The NHS says you may notice:

• A persistent low mood that does not lift with rest, a good day or a weekend.
• A loss of pleasure or interest in normal everyday activities, including things you used to enjoy.
• Feeling irritable, snapping at small things or feeling on edge.
• Feelings of despair, guilt and worthlessness, or a persistent low self-esteem.
• Tearfulness and feeling stressed or anxious.
• A reduced sex drive, and becoming less sociable, cancelling plans you would once have kept.

On top of those, SAD has a set of extra symptoms that are almost a signature of the winter form. In addition to the depression signs above, the NHS says you may also:

• Be less active than normal, moving less and doing less.
• Feel lethargic and sleepy during the day, lacking in energy even after a full night.
• Sleep for longer than normal and find it hard to get up in the morning, needing the alarm twice and still feeling groggy.
• Find it difficult to concentrate, with reading, work or conversations feeling harder than they should.
• Have an increased appetite, often with a particular craving for foods containing lots of carbohydrates, and end up gaining weight as a result.

Clinicians sometimes point out that this last cluster runs in the opposite direction from classic depression. Where typical depression brings insomnia and loss of appetite, winter SAD often brings oversleeping and overeating. That hibernation-like pattern: sleeping more, eating more, moving less, withdrawing socially, is one of the reasons people mistake it for laziness or a character flaw rather than a treatable condition. It is neither. It is a recognised medical pattern, and it responds to treatment.

Why darker evenings can affect mood

The honest answer is that the exact cause is not known. The NHS says SAD is thought to be linked to reduced exposure to daylight during the autumn and winter months, which affects the body’s internal clock and the production of certain hormones, making it harder to regulate mood and sleep.

One widely discussed theory is that the fading light changes the levels of melatonin and serotonin in the brain. Melatonin is the hormone the pineal gland produces in response to darkness, making you sleepy; as winter days grow darker, production rises, and people with SAD may feel sleepy and lethargic beyond what the season demands. Serotonin, the brain chemical involved in balancing mood, is believed to run lower in some people when sunlight fades: one line of research found higher levels of the serotonin transporter protein in winter, which would leave less serotonin active in the brain.

This is a theory, not a settled fact. No single mechanism accounts for every case, and experts are careful to say so. But it is consistent with what the clock change does this weekend: the abrupt shift to dark evenings is exactly the kind of light cue the body clock notices. Population studies around the autumn clock change have even found measurable, if small, dips in anxiety, depression and sleep-disorder events in the week after it, which our companion clock-change article explores in detail.

SAD or just the winter blues?

Not every mood dip is seasonal affective disorder, and the distinction matters because it decides what help you need. Many people feel a bit flatter, tireder and less sociable in winter. When those feelings are milder, fewer in number and do not seriously disrupt work, relationships or daily life, clinicians sometimes describe it as subsyndromal SAD, the winter blues rather than the disorder.

The dividing lines are persistence, pattern and impact. SAD means several depression symptoms present for at least two weeks at a time, recurring at the same season, and severe enough to make everyday activities increasingly difficult. The winter blues means a gentler, broader seasonal slump that lifts without treatment.

If you are unsure which camp you fall into, that uncertainty is itself a reason to talk to your GP rather than to self-diagnose. A short conversation can separate a rough patch from a recurring pattern, and the GP’s job includes exactly that judgement.

How seasonal affective disorder is diagnosed

A diagnosis of SAD is only made when the seasonal pattern is clear and repeated. Under the criteria clinicians use, the depressive episodes must begin at a regular time of year and fully remit at a characteristic time of year, the pattern must have appeared across at least two consecutive years with no non-seasonal episodes in that period, and seasonal episodes must substantially outnumber non-seasonal ones across the person’s life. A single low winter, however miserable, does not meet the threshold: the criteria deliberately separate a genuine recurring pattern from ordinary seasonal changes in mood.

In practice, a GP will usually ask about your moods and how they change across the year. Keeping a simple diary of mood, sleep and appetite through the autumn and winter can make that conversation much more useful, because the pattern is the diagnosis. The GP may also run blood tests to rule out other conditions that mimic SAD symptoms, such as an underactive thyroid or anaemia, before settling on the seasonal diagnosis.

What the NHS says helps: the treatment ladder

The NHS lists four main approaches to treating SAD, and the usual order starts with the simplest:

• Lifestyle measures: getting as much natural sunlight as possible, exercising regularly and managing stress levels. Daylight, even on an overcast day, is far brighter than indoor light, so a daily walk in the morning light does real work.
• Light therapy: using a special lamp called a light box to simulate exposure to sunlight, typically sitting near it for a set period each morning.
• Talking therapies: such as cognitive behavioural therapy or counselling, which build coping skills for the depressive thoughts the season brings. You can self-refer to NHS Talking Therapies online without going through your GP first.
• Antidepressant medication: such as selective serotonin reuptake inhibitors (SSRIs), for more severe or persistent cases, prescribed by your GP.

These are often combined. Research on combined approaches has found that pairing therapies, for example light therapy with cognitive behavioural therapy, can outperform either one alone. Your GP will tailor the mix to how severe your symptoms are and how they have responded in previous winters.

Light therapy: what the specifics are

The SAD lamp is probably the most talked-about SAD treatment, and it deserves a clear-eyed look. The usual routine is sitting next to a special lamp for 30 minutes to an hour each morning, at a brightness of around 10,000 lux, roughly the intensity of direct morning sunlight and far above ordinary indoor lighting. The idea is to compensate for the missing daylight and help the brain regulate the body clock and brain chemicals on dark mornings.

Two cautions from the clinical guidance. First, speak to your GP before buying a lamp, because light therapy is not right for everyone: people with certain eye conditions or on medication that increases light sensitivity need advice first. Second, the National Institute for Health and Care Excellence has noted that the evidence for light therapy’s effectiveness is unclear, and it is not available on the NHS, so lamps are self-funded. The NHS still lists light therapy among its recommended treatments, but it is a considered choice to make with a clinician, not an impulse purchase.

None of this is a substitute for the free option: real daylight. A brisk morning walk, a desk moved near the window, lunch eaten outside while the light lasts. These cost nothing, carry no side effects, and sit at the base of the NHS treatment ladder for a reason.

A plan for the dark-evenings week

The clocks change this Sunday. Here is a practical plan for the week that follows, built from the NHS ladder above:

• Chase the morning light. For the next few months, daylight is a morning resource: get outside within an hour or two of waking, even when it is grey. Open the curtains the moment you get up.
• Move the exercise outdoors. An hour of morning exercise has been shown to cut depressive symptoms substantially in people with SAD; do it outside and you get the daylight dose at the same time.
• Keep a regular sleep time. SAD tempts you to sleep in and stay up late. A fixed wake time, even at weekends, keeps the body clock steadier than the extra hour in bed suggests.
• Keep the social plans. Withdrawal feeds the low mood. Make one plan a week that gets you out of the house in daylight or with other people.
• Mind the darker evenings practically too. Dark evenings mean more candles, lamps and heaters: keep candles out of children’s reach and treat tea lights with the same caution as any open flame. If the worst happens, our guide to what to do for a burn at home covers the 20 minutes that decide how well a burn heals.
• Track your mood. A one-line nightly note (mood out of ten, hours slept, appetite) takes thirty seconds and is gold dust at a GP appointment.

Sleep deserves its own mention here. SAD often brings oversleeping and groggy mornings, and the clock change itself briefly disrupts sleep patterns: our companion piece found that people sleep roughly half an hour longer on the clock-change Sunday itself. If broken or excessive sleep is your main symptom, you may also find our article on the sleep problem linked to a 26 percent higher stroke risk useful background, though insomnia and SAD point in opposite directions.

When to see your GP

The NHS advice is direct: see your GP if you think you might have SAD and you are finding it difficult to cope. There are helpful treatments a GP can recommend, and you do not need to wait until you meet a formal definition of the disorder.

Book the appointment if the low mood has lasted most days for two weeks or more, if it returns every autumn and winter, if it is affecting your work or relationships, or if you are using alcohol or other coping strategies that worry you. If you ever feel unable to keep yourself safe, contact NHS 111, or call Samaritans on 116 123, which is free and open around the clock.

Sunday brings dark evenings whether we like it or not. What we can choose is whether we treat the mood dip that follows as a personal failing or as what the evidence says it is: a recognisable, diagnosable and treatable pattern. The symptoms of seasonal affective disorder are well described, the treatments are well established, and the first step is a conversation with your GP. Dark evenings end. With the right help, so does the low mood that comes with them.

Frequently asked questions

What are the main symptoms of seasonal affective disorder?

The NHS lists a persistent low mood, loss of pleasure or interest in everyday activities, irritability, feelings of despair, guilt and worthlessness, low self-esteem, tearfulness, anxiety, reduced sex drive and becoming less sociable, plus SAD-specific signs: being less active, daytime lethargy, sleeping longer than normal and struggling to get up, difficulty concentrating, and increased appetite with carbohydrate cravings and weight gain.

How do I know if I have SAD or just the winter blues?

SAD means several depression symptoms present most days for at least two weeks, recurring at the same time of year and severe enough to disrupt daily life. The winter blues is a milder, broader seasonal slump that lifts without treatment. If you are unsure, a GP can help tell the two apart.

What causes seasonal affective disorder?

The exact cause is not known. The NHS says it is thought to be linked to reduced exposure to daylight in autumn and winter, which affects the body’s internal clock and the production of hormones such as melatonin and serotonin that regulate mood and sleep.

How is seasonal affective disorder diagnosed?

A GP will ask about your moods and how they change across the year. A formal seasonal-pattern diagnosis requires depressive episodes that begin and end at a regular time of year across at least two consecutive years, with full remission in between. Blood tests may rule out other causes such as an underactive thyroid.

Does light therapy work for seasonal affective disorder?

The NHS lists light therapy, sitting near a 10,000-lux light box for 30 minutes to an hour each morning, as a treatment option. However, the National Institute for Health and Care Excellence notes the evidence for its effectiveness is unclear. Speak to your GP before buying a lamp, and remember that free daylight and exercise sit at the base of the treatment ladder.

When should I see a GP about my mood?

See your GP if you think you might have SAD and are finding it difficult to cope, especially if low mood has lasted most days for two weeks or more, returns every autumn and winter, or is affecting your work or relationships. If you feel unable to keep yourself safe, call NHS 111 or Samaritans on 116 123.

Sources

• NHS 111 Wales, Seasonal affective disorder: symptoms, treatment and when to see your GP. https://111.wales.nhs.uk/encyclopaedia/S/article/Seasonalaffectivedisorder?locale=en
• timeanddate.com, Daylight Saving Time Changes 2026 in the United Kingdom (clock change Sunday 25 October 2026, 2am). https://www.timeanddate.com/time/change/@51.27833,1.07750
• Child Mind Institute, What Is Seasonal Affective Disorder? (diagnosis: at least two consecutive years of seasonal episodes; symptoms). https://childmind.org/article/seasonal-affective-disorder/
• GoodTherapy, Seasonal Affective Disorder (SAD): Understanding and Managing Seasonal Depression (DSM-5-TR criteria; light therapy protocol 2,500 to 10,000 lux). https://www.goodtherapy.org/simpleview.html?simpleview_topic=seasonal-affective-disorder
• NHS tips for tackling seasonal affective disorder, via The Free Library (light therapy 30 minutes to 1 hour each morning; NICE notes evidence unclear; treat as other depression). https://www.thefreelibrary.com/NHS+tips+for+tackling+seasonal+affective+disorder%3b+The+condition+is…-a0725353564
• NAViGO Care, Seasonal Affective Disorder (NHS Talking Therapies self-referral; crisis support). https://navigocare.co.uk/what-we-do/advice-and-support/seasonal-affective-disorder

Related reading

• The Clocks Go Back in Four Days: What the Extra Hour Does to Your Health
• What to Do for a Burn at Home: The 20 Minutes That Decide How Well It Heals
• The Sleep Problem Linked to a 26% Higher Stroke Risk

Medical disclaimer: this article is for information only and is not medical advice. If you are struggling with low mood, see your GP. If you feel unable to keep yourself safe, call NHS 111 or Samaritans on 116 123.