Why do I get depressed without anything stressful happening to me?

For individuals who have unipolar major depression, an episode can be triggered by internal stressors like anger, fear, fatigue, and natural hormonal changes, or external stressors such as sickness and overwork. You do not have to experience any single big event to trigger a depressive episode; several moderate stressors can add up to a big load of stress. And once an episode of depression starts, it increases the stress reaction in the brain. After you have the first episode of unipolar major depression, others come more easily.