Sometimes we say: I am really depressed today, or I am not in the mood to see other people or to go out etc. This feeling of "depression" is more than normal to experience. We are allowed to feel sad, nervous, stressed, angry or have other "negative feelings". Actually biologically we tend to experience more "negative" than "positive" emotions and the explanation for that arises from an evolutionary point of view. By having "negative" emotions we are preparing ourselves to be alarmed and by being alarmed we survived from a lot of situations.
Nowadays, we assume that is not good to feel sad and we have learnt that being "happy" is more "in" fashion. Why do we actually think that? Have you ever noticed how happy are the couples in television? Or have you ever realised that everybody is posting happy moments on media? Every single person that have a well-functioning smart phone has noticed that. Often we subconsciously are jealous for what we see and we would like to be that happy. As a result we tend to cover our sadness or other "negative" emotions because we also want to appear so happy in frond of others. Whoever is reading this can easily assume that is of course better to feel happy than sad, despite the idealisation of life by media. I would say that it is better to feel happy most of the time but it is also healthier to feel sad and not to push that "bad" feeling away. When you have negative emotions you are re thinking situation and you may equip yourself with better solutions in case another similar situation happens. Moreover, when you are covering those "negative" emotions they will not go away but they will gather inside formulating a huge negativity that is a lot more difficult to deal with. With other words, is better to realise why we are feeling sad by the time we are experiencing a problem rather than covering it. The accumulation of "negative" emotions means accumulation of problems and this can often cause depression. Depression according to American Psychological Association is a common and serious and medical illness that negatively affects how you feel, they way you think and how you act. Depression can vary from mild to severe depending on someone's symptomatology. Fortunately is treatable and the best way to treat it, is first of all to realise it and secondly to seek for help.
The symptoms of depression according to DSM (diagnostic statistical manual) are:
Persistent sad or anxious mood
Loss of appetite and/or weight loss, or conversely overeating and weight gain
Restlessness or irritability
Insomnia or hypersomnia
Feelings of worthlessness, inappropriate guilt, helplessness
Feelings of hopelessness, pessimism
Difficulty thinking, concentrating, remembering or making decisions
Fatigue, loss of energy
Decreased interest in pleasurable stimuli (sex, food, social interaction)
Thoughts of death or suicide or attempt at suicide
In order for the diagnosis to be done at least 5 symptoms need to be present and to be persistent for at least two weeks. These symptoms should affect normal life functioning. Not everybody is showing the same symptoms which means that each person is unique and needs to be examined individually. A few factors (environmental or biological) can be counted as possible causes but nothing is clear yet.