Most of us have moments or short periods of sadness when we feel lonely or depressed. These sensations are usually normal ones that sometimes occur in life. They can be the result of a recent loss, having a particularly challenging day or week, or a reaction to a hurtful comment. However, when feelings of sadness and being unable to cope overwhelm the person, so much so that they undermine their ability to live a normal and active life, it is possible that they have what is known as a major depressive disorder (MDD), also called clinical depression, unipolar depression or major depression. Informally, the condition is simply referred to as depression. Depression can have a major negative impact on a sufferer\'s life - experts say the effect is comparable to that of diabetes, and some other chronic conditions. Depressive symptoms vary significantly between people. Most commonly, the person with depression feels hopeless, sad, and has lost interest in doing the things that were once pleasurable. What is the difference between a sign and a symptom? - A symptom is something felt by the patient, such as a headache, while a sign is detected by other people too, such as a rash. Below are some signs and symptoms associated with depression: Psychological signs and symptoms: Persistent sadness or low mood Thoughts and feelings of worthlessness Feelings of self hatred A feeling of hopelessness A feeling of helplessness Feeling like crying A feeling of guilt Irritability - even trivial things become annoying Angry outbursts Intolerance towards others Persistent doubting - finding it very hard to decide on things Finding it impossible to enjoy life Thoughts of self harm Thoughts of suicide Persistent worry Persistent anxiety Physical signs and symptoms Body movements may be slower than they used to be Problems with focusing, the person\'s concentration span may be reduced Speech may be slower than it used to be Eating patterns change, appetite changes - typically, the patient eats less and loses weight. However, some people may eat more and gain weight. Low sex drive Lack of energy, fatigue, tiredness - even small and easy chores feel like unpleasant ordeals The woman\'s menstrual cycle may change Restlessness - the patient may pace up and down more, wring his/her hands, and find it hard to keep still Unexplained aches and pains, such as headache, backache or digestive problems Sleeping disturbances - the individual may find it hard to get to sleep, or wakes up during the night and cannot get back to sleep. Studies have shown that over 80% of people with depression suffer from some kind of insomnia. Hypesomnia (oversleeping) is also possible. Some medications used for treating depression may cause insomnia. Social signs and symptoms may include: Underperforming at work Not doing well at school Avoiding keeping in touch with friends Abandoning interests and hobbies Having family/home problems In severe depression, the patient may experience symptoms of psychosis - delusions or hallucinations (less common).