A state of altered perception where one sees the world as bleak and dark. Feelings and actions such as purposelessness, disinterest, low self esteem, self-harm
, pessimism, suicidal thoughts or tendencies and a lack of motivation or energy may accompany it. It is not simply the feeling of being sad, but is a lasting state of mind that could be caused by a number of factors. Many health problems lead to depression, poor sleeping habits or eating habits, stress, drugs. Somebody who lives a life of abuse or poverty would be a victim of depression. Clinical depression is a very serious problem, and those who have it should seek help. Often it is difficult to recognise due to the numbness it can bring, and usually people are not willing to admit when they are depressed. Depression is difficult to imagine when one is not depressed, and can therefore fall under the critical eye as something that does not exist and something people only whine about because they have nothing better to do. Nobody can know for certain what another person is feeling, so it is not something anybody can judge.
Your next door neighbour seems happy and normal. You find out he has killed himself. Nobody had suspected his depression, but he has been feeling alienated and could find no sense of living, the pain and torment he was secretly feeling were too much to take.