###Human: I feel sad most of the time. Do not know, why. Please help. ###Assistant: Hi. The details you have provided about your problem are very brief. Although, if you have these problems for more than two weeks then you are probably suffering from a major depressive disorder. A major depressive disorder is a condition in which patients develop sadness lasting an entire day for at least two weeks. It also has restlessness, loss of energy, hopelessness, worthlessness, and loss of self-esteem. For your symptoms, you need to meet a psychiatrist in person or online, whichever is convenient. He will ask you a few more details about your problem including family history. After this, he will decide the further course of action appropriate for you, like medication or talk therapy.