"Many people suffer temporary melancholy in the autumn. It's part of life and not depression in the medical sense," says Ulrich Hegerl of the Leipzig-based German Research Network on Depression and Suicidality.
There are four main reasons for the autumn blues.
"For one thing, there's the psychological component, whereby most people have negative associations with darkness. That has evolutionary and genetic causes," says Ruediger Schmitt-Homm, a physiologist with the German Green Cross in Marburg.
The physiological reasons for the autumn blues are more complex. There are three biological connections that negatively affect the human mood.
For one thing, less sunlight travels from the eyes to the brain during autumn.
"That reduces the production of serotonin, which promotes contentment and balance," says Schmitt-Homm.
The longer nights and darker days mean more melatonin is produced for the body's day-night rhythms. "That causes the rhythm to even out, making people sleepier."
Lastly, the body does not get enough Vitamin D, which is usually produced by sunshine on the skin. A high level of Vitamin D can help fight depression.
Schmitt-Homm recommends people go to their front door in the early morning to soak up some daylight. "Ten minutes under cloudy skies should be enough to perk up serotonin levels."
Full-spectrum Biolight lamps are another alternative. Getting up early also improves the mood. People who sleep late use a lot of serotonin in their sleep phase for dream activity right before waking.
"Early 'birds' are much more stable, psychologically."
Vitamin D levels can be stabilized by eating plenty of fish and supplements. Along with Vitamin D, fish also offer omega 3 fatty acids, which can also improve moods.
"You can spread a tablespoon of linseed oil, hempseed oil or even rapeseed oil over a salad and improve your mood," explains Schmitt-Homm.
Exercise can also lift spirits. "You don't have to do it for hours, but enough so that you break a sweat."
It's also important to keep a positive outlook in the autumn, advises Horst Conen, a personal and lifestyle management trainer from Cologne.
"You can take a little time in the morning and put together a ritual to get yourself ready for the day. Taking a stroll through the garden, for example." It's also helpful to think about autumn's positive sides. "You can think about a trip to a forest, about winter fashions or autumn's great cultural events."
"There are positives to a blue mood," says Hegerl. "The blues are pretty nice. Then you're introverted. It can be a nice balance to the extroverted summer."
Regular breaks can make it easier to manage a day lacking in motivators. "A coffee break in your favourite cafe or calling a friend in the afternoon" are both recommended by Conen.
There are also a lot of wonderful moments to savour in the autumn. "Every morning, put a handful of dry beans in your left pocket, and, for every good moment, move one bean from the left to the right pocket," advises Conen. "That makes the good moments tangible."
Most people get over seasonal depressions. Seasonal Affective Disorder (SAD) plays a role in a small number of cases.
"Only about 10 percent of all depression cases in the autumn and winter are linked to this," says Hegerl. Sufferers crave sleep and have large appetites. If the symptoms last for more than two weeks and there's a noticeable psychological strain, seek medical advice.