The symptoms of SAD usually recur regularly each winter,
starting between September and November and continuing
until March or April.

A diagnosis can be made after three or more consecutive winters of symptoms, which may include a number of the following:

Depression

• Low mood, worse than and different from normal sadness
• Negative thoughts and feelings
• Guilt and loss of self-esteem
• Sometimes hopelessness and despair
• Sometimes apathy and inability to feel

Sleep Problems

• The need to sleep more
• A tendency to oversleep
• Difficulty staying awake during the day and/or disturbed sleep with
  very early morning wakening

Lethargy

• Fatigue, often incapacitating, making it very difficult or impossible to carry out normal routines

Over Eating

• Craving for carbohydrates and sweet foods leading to an increase in weight

Cognitive Function

• Difficulty with concentration and memory
• The brain does not work as well, or as quickly

Social Problems

• Irritability
• Finding it harder to be with people

Anxiety

• Tension
• Stress is harder to deal with

Loss of Libido

• Less interest in sex and physical contact

Sudden Mood Changes in Spring

• Sharp change in mood
• Some experience agitation and restlessness and/or a short period of
  hypomania (over activity)
• No dramatic mood change but a gradual loss of winter symptoms

Most sufferers show signs of a weakened immune system during the winter,
and are more vulnerable to infections and other illnesses.

SAD symptoms disappear in spring, either suddenly with a short period (e.g. four weeks) of hypomania or hyperactivity, or gradually, depending on the intensity
of sunlight in the spring and early summer.

In sub-syndromal SAD, symptoms such as tiredness, lethargy, sleep and eating problems occur, but depression and anxiety are absent or mild.

SAD may begin at any age but the main age of onset is between 18 and 30 years.
SAD occurs throughout the northern and southern hemispheres but is extremely rare in those living within 30 degrees of the Equator, where daylight hours are long, constant and extremely bright.