"I felt completely numb. I stopped seeing my children as children, I could no longer have fun with them or go on trips with them. I was a miserable wretch," says Thomas Müller-Röhrich.

He felt the first signs of depression in 1992. It was as if he could no longer do his work. He's a self-employed computer programmer. Müller-Röhrich started to withdraw - he didn't want to talk to people, and just waited until the days would end.

His story is common. About four million people suffer from depression in Germany alone. It's an illness like any other.

Depression attacks the functions of the brain. It controls our happiness, our sadness, and our ability to sleep. People with depression lack motivation. It can lead to sleep disturbances, a loss of appetite, weight loss, hopelessness and a sense of guilt, dark thoughts, doubt and suicide.

But before a diagnosis can be made, doctors say a patient has to have experienced a variety of these symptoms for up to six week - but at least for two weeks. Only then can one speak of depression, says Professor Ulrich Hegerl, the director of the Leipzig Clinic for Psychiatry.

"A person suffering depression can feel no grief, the whole things is just wretched and hopeless," Hegerl says. "If you have cancer, or another illness, you can still have hope and want to make the most of your time. But pain is so great for people with depression that many commit suicide."

People with depression often have a permanent sense of alarm - they are constantly tense.

"The stress hormones are out of balance," says Hegerl.

Long road to diagnosis

But many people don't know what to do when such symptoms first present themselves.

Some people believe they have contracted a serious viral infection, or some other illness.

And some think their inability to sleep is the very reason they feel so ill. But the insomnia is itself a symptom of depression.

Thomas Müller-Röhrig says the best thing you can do is get informed - as quickly as possible. There are self-help groups, such as the "Deutsche Depressionsliga" (German Depression League), of which he is the chair.

"More and more people with depression seek help - and doctors are getting better at understanding the symptoms," says Müller-Röhrig.

Depression and suicide

"Above all, depression is called by its name these days and is described as such."

So the good news is that more people are diagnosed with depression than 30 years ago. At the same time, suicide rates have fallen. From a high of 18,000 suicides per year in Germany, the number has fallen to 10,000.

Thirty years ago, eight percent of the population took early retirement because of psychological problems. Today, the rate is 42 percent.

But Hegerl says this doesn't mean the number of people with depression has risen.

"People used to face discrimination because of mental problems, so doctors made other diagnoses. But that's no longer the case," Hegerl says.

Psychotherapy and anti-depressives

Anti-depressives remain a common form of treatment. The same goes for some forms of psychotherapy, including cognitive behavioral therapy (CBT). The idea with CBT is to lend the day a clear and balanced structure.

And so it was for Müller-Röhrig. His diagnosis came as a relief. He finally knew what he was suffering from and what he could do about it.

"There are various forms of therapy - they may include a bit of sport, painting, handicrafts, or going for walks," Müller-Röhrig says.

The right amount of sleep

A lot of people believe sleep is good for treating depression. People with depression often go to bed early, because they think they need a good night's sleep.

But the opposite is true.

"They're exhausted," says Hegerl. "But not sleeping acts as an anti-depressive. Studies have shown this, and it's very effective. When patients stay awake for the second half of the night, we've seen an improvement in the early hours of the day in 60 percent of cases."

For Thomas Müller-Röhrig, anti-depressive medication has helped over the past 20 years. At first, he rejected the idea of taking medication, because while he knew it might improve his situation, he felt it wouldn't really change anything.

Today, he sees things differently.

"In some cases, it may not be enough to change your behavior," he says. "Sometimes you have to compliment your treatment with medication."

Müller-Röhrig has been back working at his company for years now. He says he has a grip on his life again, and he works closely with the "Deutsche Depressionsliga." He has this advice: if you think you have the symptoms of depression, don't keep putting it off, get help from a doctor. If you don't, it will only get worse.

October 1 is European Depression Day.