EVERYONE experiences some sort of unhappiness from time to time, and it's often triggered by a traumatic event such as the break-up of a relationship or bereavement.

Most people also feel down from time to time, but this unhappiness can develop into a bout of depression, which is a real illness that often goes unrecognised.

Depression affects up to 40 per cent of people at some point in their lives, and it is twice as common in women as in men.

It often appears first during the teens or twenties. Some people then experience recurrent episodes throughout their lives.

The most common symptom is low mood. In addition to feeling sad, some people are irritable and tend to lose their temper more easily than usual. Often, people notice that they feel worse either first thing in the morning or last thing at night.

Depressed people find that they can't get pleasure from events or activities that they normally would. They tend to feel different and separate from the rest of the world.

Lack of energy, tiredness and poor concentration are also common symptoms.

Sufferers also find they don't sleep well, either waking up un-refreshed from a long sleep, or waking up very early in the morning. Loss of sex drive (libido) and disturbed eating patterns either loss of appetite or eating too much are also common.

Symptoms of anxiety routinely occur with depression. People may experience fearfulness, palpitations and even panic attacks. Very often these feelings subside when the depression is treated.

One of the most serious aspects of depression is the thoughts people have about themselves. Sufferers start to judge themselves excessively harshly or critically.

They may think of harming themselves or feel that life is not worth living.

People who are depressed are more likely than others to attempt suicide, and many people with depression turn to alcohol or illegal drugs to try and blot out their difficult feelings.

Usually a bout of depression is set off by a stressful event, often involving some form of loss. This may stem from a death or from the breakdown of a relationship.

Financial worries, a stressful job, redundancy or fear of unemployment, even moving house, can trigger depression in vulnerable people.

New mothers are susceptible to postnatal depression. And long-term or serious illnesses, such as diabetes or cancer, can also trigger depression.

Relationship problems are common in depressed people. These may be part of the cause of a person's depression or a consequence.

Some forms of the illness seem to run in families, but researchers have yet to find a simple genetic explanation.

Unhappy childhood experiences have been shown to be important in the development of depression in adult life.

For example, a child who loses his or her mother before the age of 14 and lacks adequate care from another person is more likely to develop depression. Other difficult childhood events, such as sexual abuse, are linked to depression in adult life.

Lastly, some people just tend to look at the darker side of things. These people are more likely to develop full-blown depression at some point in their lives.

Depression interferes with the way people want to live their everyday lives. And, yet, many sufferers never seek help, either because they're embarrassed by their feelings, see them as a sign of weakness or blame themselves for their misfortunes.

Fortunately, a number of treatments are available for depression and talking to a qualified professional about feelings is the first step.

By asking specific questions about your mood, sleep patterns, appetite, libido (sex drive) and energy levels, most GPs can diagnose depression.

They may ask more about what is happening in your life that would help to explain the feelings you are experiencing.

For mild forms of depression, psychological treatments are often sufficient. For more severe depression, a combination of psychological treatment and antidepressant drugs, or antidepressants alone, is usually recommended.

Regular physical exercise may also be helpful for mild to moderate depression.

If you would like to talk to Dr Ali or to one of the GPs within the team based at the BUPA Roding Hospital, call 0808 1447324 to make an appointment or alternatively email him; dr.ali@u-firsthealthcare.co.uk.