Most people feel sad or blue at various points in their lives, but those who remain in a depressed mood for most the day, nearly every day, may be in the grips of severe depression, also known as clinical depression. Severe depression can affect people in a variety of ways, and a person's age, gender, personality traits and cultural background can influence how a person reacts.Sustained SymptomsSevere depression affects the way people think, sleep and eat, and substantial changes in those areas are often the first sign that a depression has become severe. The primary sign of a severe depression, however, are symptoms that exhibit themselves for a prolonged period of time. When the following symptoms occur for at least two weeks, severe depression may be the cause:General Signs of Severe DepressionInsomnia or excessive sleepingDisinterest in activities that were formerly enjoyedFatigue or loss of energyImpaired concentration Marked indecisivenessReduced sex driveChanges in appetiteWeight gain or lossFeelings of sadness or unhappinessFeelings of guilt, despair, shame or worthlessnessFeelings of irritability or frustrationRestlessness or sluggish movementUnexplained physical symptoms, such as headaches or Back painRecurring thoughts of suicide or deathSevere Depression in Children and TeenagersYoung children with severe depression may exhibit emotions like sadness, irritability, worry and hopelessness. Teenagers may display anger and anxiety or may seek to isolate themselves from the outside world.Severe Depression in Older AdultsSevere depression in older adults often goes undiagnosed. Many mistakenly assume that fatigue, a reduced sex drive, loss of appetite and sleep problems accompany the aging process. Seniors may exacerbate severe depression by avoidance and withdrawal.Other signs of severe depression include an inability to alter one's mood through will or determination. Support is usually needed to cure severe depression. Talking to a friend, loved one, health care professional, doctor or member of the clergy can help those with severe depression. Untreated severe depression can lead to other mental and physical health problems. When severe depression is accompanied by thoughts of suicide, immediate emergency intervention is indicated.