First of all let’s make this clear: “Nervous Breakdown” is a popular term, it is not a clinical term and is not used by mental health professionals. Nervous Breakdown (or Mental Breakdown) is a term used for a severe, time-limited psychiatric disorder that can cause a previously functional person to break down to the point that they are no longer functional day-to-day. These breakdowns are usually temporary in nature and are often tied to some form of psychological burnout due to overwork, sleep deprivation, increased stress, decreased health, or a combination of these things.
The term can be used to describe any number of mental disorders that a person may experience. It is used for a number of reasons, including: to hide a diagnosis; to avoid the stigma of a diagnosis; not understanding the reasons for certain loss of function (such as not seeing a doctor, but having symptoms); and not accepting a diagnosis among others. There are many disorders that can fit within the criteria of “Nervous Breakdown”, but those that most commonly occur are those related to:
The Disorder that is mimics the most directly however is Major Depressive Disorder (Depression). On the historical note, the reason the term “Nervous Breakdown” came into being was that people preferred to have a physical (Nerves) illness as opposed to a psychological or psychiatric illness.