A nervous breakdown, also known as a mental breakdown; is a sudden, acute attack of mental illness such as depression or anxiety. Like sanity, the term is not recognized by the psychological community. In part, this is because the term has pejorative connotations, while this phenomenon is a normal and relatively common response to chronic stress. Often, the emerging illness is only described as a "breakdown" when the person becomes unable to function, at which point the disorder is advanced. Often, the supposed breakdown is a manifestation of career burnout. The psychiatric community rejects the term "nervous breakdown", in part, because it is not descriptive enough of the actual disorder and symptoms. A common diagnosis that follows such an event is brief reactive psychosis Clinical depression is a state of sadness, melancholia or despair that has advanced to the point of being disruptive to an individual's social functioning and/or activities of daily living. Although a low mood or state of dejection that does not affect functioning is often referred to as depression, clinical depression is a medical diagnosis and is different from the everyday meaning of "being depressed". thats the difference hoped this helped !!