Depressive episodes are dominated by a depressed mood, which is not proportional to its situation and can range from moping to grief and even malaise. In severe cases, psychotic symptoms such as hallucinations and delusions may occur. Anxiety and motor agitation are significant in some cases. Depressive episodes are characterized by depressed mood as the main clinical manifestation, 1. loss of interest and unpleasant feelings, 2. loss of energy or fatigue, 3. psychomotor retardation or agitation, 4. low self-esteem, self-blame, or feelings of guilt, 5. difficulty in association or reduced ability to think, 6. recurrent thoughts of death or suicidal or self-injurious behavior, 7. sleep disorders such as insomnia, early awakening, or 8. decreased appetite or significant weight loss; 9. decreased sexual desire. This is the most core symptom of depression. The milder ones are sullen and unpleasant, while the heavier ones are painful, pessimistic and desperate, and life is worse than death. This is the biological characteristic of depression. On the basis of depressed mood, patients will have lower self-evaluation, sense of uselessness, hopelessness, helplessness and worthlessness, often accompanied by self-blame and self-guilt. In severe cases, delusions of guilt and paranoia may appear, and some patients may experience hallucinations, delusions, and other symptoms of schizophrenia, noting that some patients may experience extended suicide. 2. Delayed thinking: Patients think and consider things more slowly, are less responsive, and feel that their “brain is rusty” and “like a layer of paste”. Clinically, it can be seen that the speech is significantly reduced, the speed of speech is significantly slowed down, the voice is low, and it is difficult to answer, and in serious cases, communication cannot be carried out smoothly, giving the impression that the patient has become stupid. 3.Decreased volitional activity: Patients with severe depression show significant and persistent decrease and inhibition of volitional activity, such as slow behavior, passive and lazy life, poor personal hygiene, bed-ridden, living alone behind closed doors, treating relatives coldly, avoiding social life, not wanting to do anything, not wanting to contact and interact with people around, often sitting alone. In severe cases, even food, drink and other physiological needs and personal hygiene are disregarded, unkempt and unkempt, and even develop into non-verbal, non-moving, non-food, called “depressive rigidity”. 4, suicidal concept: Severe patients often have the concept or behavior of suicide, thinking that living is too painful, and death is the best relief, also think that “they live in the world is redundant”, will make suicide attempts to develop into suicidal behavior. The emergence of suicidal ideas and behaviors indicates that the patient’s condition is serious and needs to be closely monitored and promptly seen by psychiatry and psychiatric departments, and if necessary, hospitalized. 5, cognitive impairment: depressed patients have cognitive impairment: memory loss, learning difficulties, attention deficit, prolonged reaction time, poor abstract thinking ability, poor language fluency, spatial perception, eye-hand coordination and thinking flexibility, etc. In severe cases, it seems like dementia patients, called “pseudo-dementia “Pseudo-dementia”. 6. Somatic symptoms: Why do most depressed patients not go to psychiatry but consult internal medicine and other non-psychological and psychiatric departments? It is because depressed patients often have a lot of physical complaints, internal medicine and other doctors often do not identify, the patient will not think they are depressed, just feel physically uncomfortable, we are often reluctant to admit that there is a mental illness, willing to admit that there is something wrong with the body, worried about mental illness and discrimination. Somatic symptoms are common: sleep disorders (difficulty falling asleep, early awakening) digestive symptoms (nausea, vomiting, constipation), pain in any part of the body, cardiovascular symptoms (panic, chest tightness, sweating), etc. The complaints of somatic discomfort can involve all organs, and symptoms of autonomic dysfunction are also more common. Early awakening in sleep disorders is defined as waking up 2-3 hours earlier than usual and not being able to go back to sleep after waking up. Early awakening and constipation are biological features of depressive episodes, as well as significant loss of appetite and libido, and some female patients also have menstrual disorders (delayed, stopped menstruation, low menstrual flow).