I should preface my explanation of depression by saying that this is just 1 way of looking at what is quite a complicated discussion. Depression has many social and individual influences. Nevertheless, having spoken to people about it for more than a decade, this is the way I explain it.
When bad or distressing things happen they cause unpleasant emotions. This is normal. However, sometimes things get out of control, the emotions cause us to behave differently, often doing less enjoyable things, and this feeds on to further negative emotions. Eventually it can cause a situation whereby our emotions cloud the very perception of what is actually happening in reality. We start to perceive things to be negative even when they may not be. This is depression. When it happens with a clear situational trigger (ie a stressful event in life) it is called ‘reactive depression.’ Sometimes there is no clear initial trigger for the first negative emotions, but depression has built up all the same; this is called ‘endogenous depression.’
Sometimes the negative emotion is more anxiety than sadness. In reality there is very often some degree of both anxiety and sadness in this kind of mood problem. The diagnoses differ accordingly (achieving labels of ‘depression,’ ‘anxiety’ and ‘anxiety with depression’), but the basic underlying causes are the same.
Now, people generally know that drinking too much alcohol makes the liver fail. The liver’s job in the body is to break down chemicals, one of which is alcohol. However, if you ask your liver to do too much by giving it more alcohol that it can break down, it starts to malfunction.
Well, the brain’s job is to deal with perception: to identify what is happening in the world, order it into consciousness and choose an appropriate feeling (emotion) to associate with it. As with the liver, if you ask your brain to do too much, it starts going wrong. When this happens it makes incorrect calculations when making its assessment of reality: it starts making 2 + 2 = 5. Asking the brain to do too much is what is happening in highly stressful situations, and sometimes, if these go on for too long, 2 + 2 starts equalling 5.
When 2 + 2 = 5, our impression of what is going on doesn’t match the reality well at all. Everything is bought into on a certain emotional level (normally depressed or anxious) and the emotional response is set irrespective of the external influences. Even clearly pleasant tasks such as reading a book or walking the dogs, tasks that previously were enjoyed and can be recognised to have not changed at all from when they were enjoyed, fail to cause positive emotions. When 2 + 2 = 5, the world is bleak.
Of course, things can be made worse by the fact that the brain, the very part of the body that has started to malfunction, is the organ used to detect problems in the body. When the detection mechanisms are broken, you fail to realise that you are not experiencing emotions appropriate for the situation, and this just makes you feel worse and stops you from seeking help (as you don’t realise there’s a problem, you just think things are crappy).
Treatment for depression can be divided into 3 parts:
Firstly, if there is a cause of the depression then dealing with it will help a person adjust their thinking to make 2 + 2 = 4 again.
Secondly, we try to treat depression by looking closely at how a person is acting and thinking. As explained above, depression is caused by a spiral of negative thoughts (even if they were initially perfectly appropriate negative thoughts) causing negative emotions, and also causing a person to act in a way that reduces the potential for positive thoughts (such as losing their motivation for socialising or doing things they previously enjoyed). Thus, challenging negative thoughts, and working hard to structure time and act in a certain way can help break that cycle and lift the mood. This is one aspect of psychotherapy.
Finally there is medication. There is conflicting evidence as to the effectiveness of anti-depressant medication, but my reading of it (which matches my experience in their use) is that they can be a helpful part of treating moderate to severe cases of depression – where an extra push is needed to make 2 + 2 = 4. Anti-depressants work by increasing the availability of various chemicals in the brain. Having spoken to many people about their use, the way I see them being felt to work, is that they allow a thought to zoom around a brain a few times before being bought into on an emotional level. That way, instead of something happening, and an instant negative reaction popping up (as is the case with anxiety or depression), the brain has more of a chance to assess the reality of the situation and choose an appropriate emotional response. They allow an opportunity for the brain to be given some space to make its calculations, and thus make 2 + 2 = 4.
That is my explanation of a phenomenon that there are many explanations of. It is what you would hear if it was being discussed in my room, but it is by no means the only way of looking it.