For starters, the expression "nervous breakdown" is not a clinical term. It was popularized because people would always prefer to have a physical (nerves) problem, than a psychological or psychiatric problem, but the truth is that most of the times what people call a "nervous breakdown" is really one of the following (among others): -Panic disorder, panic attack, bipolar disorder, anxiety, traumatic stress, post-traumatic stress, psychotic disorder, depression, schizophrenia, mood disorders. In short, independently of the specific mental illness, a "nervous breakdown" is a system overload. In other words, if one has one of the illnesses listed, an overload or shock can make it worse and/or make it noticeable (as in the case of a schizophrenia or a mood disorder). You can say then that some conditions make people prone to a nervous breakdown. If you are perfectly healthy, the system overload or shock can trigger and become one the listed things (such in the case of a panic disorder or post-traumatic stress). In this case the nervous breakdown itself is the beginning of a psychological problem. So, finally we could define a "nervous breakdown" as a very strong psychological experience that shocks the person consciously or unconsciusly and shows itself immediately, progressively or eventually. Some examples: -Being a survivor of a military unit, having witnessed the death of your mates (eventual post-traumatic stress or immediate traumatic stress). -Being abused as a kid (progressive mood disorder or eventual depression). -Learning that a loved one died in a terrible accident (immediate panic attack or progressive depression). Well, you get the idea.

A nervous breakdown could also be an effect from too much stress. It may cause you to cry, scream, or have a type of mental breakdown. It's considered an overwhelming feeling from too much stress and problems from daily life and may be treated with therapy and medication.

From http://en.wikipedia.org/wiki/Nervous_breakdown Although not a medical term, the phrase "nervous breakdown" is often used by laymen to describe a sudden and acute attack of mental illness e.g. clinical depression, anxiety disorder, etc. in a previously outwardly healthy person. Breakdowns are the result of chronic and unrelenting nervous strain, and not a sign of weakness. Like any machine, the human body will start to malfunction when put under too much stress. In common usage the term "nervous breakdown" does not have a clinical definition and no reputable doctor would use it in serious diagnosis, instead focusing on definite symptoms and underlying causes. One common diagnosis used in this case is brief reactive psychosis. Some commentators claim that a nervous breakdown can actually be a good thing in the long run, because (a) it forces the person to take a proper time-out to rest and recuperate and (b) the patient will have to deal with the issues that caused the breakdown in order to recover fully. Causes of breakdown include chronic and unresolved grief, unemployment, career changes and other work stress, serious or chronic illness in a family member, divorce, death of a family member, and other sudden major life changes.

The other answers are valid, but there are physical "nerve" events taking place causing many of the symptoms of mood disorders. The brain is a factory of chemical production, and when the brain reaches a chemical equilibrium (i.e. no pain), then it knows which chemicals to produce/release in what quantities to have this positive effect. What causes a nervous breakdown is the brain being unable to discover the correct chemical combinations to relieve the problem and bring the brain back to stability, so it pretty much releases all of them. The major player is adrenalin, which is the chemical equivalent of a Marine Drill Sargent at 5AM. Adrenalin quickly heightens all of the senses, creating the famous "fight or flight" sensation. If a person were to have this sensation frequently, your "nerves" will simply become more and more sensitive, your survival instincts will become very "sharp," and before long, a simple knock on the door or a phone ringing will activate an intense survival response. One solution to a nervous breakdown is to put yourself in a situation where the chemical imbalance is appropriate, such as spending the day riding rollercoasters, or skydiving - this will "exercise" the sensation of relief.

The term nervous breakdown has been changed by the American Psychiatric Association's Naming Committee. The correct term is Dissociative Mental Break. Unknown to most people in the mental health field, designers and engineers accidentally discovered the cause of most of these events. Other answers are the current beliefs of experts in psychology and psychiatry. But the cause of these mental events has not been proved. Explanations involving stress are someone's opinion based on observation. No one has the ability to "open the box, mind," and look in to determine the cause. __________ Workers using the first close-spaced office workstations began having mental breaks. Upon investigation the problem was Subliminal Distraction caused by the subliminal detection of threat movement to effect a peripheral vision reflex. The office cubicle solved that problem after 1968. Cubicles are designed to block side or peripheral vision when a worker enters the workstation to perform office duties. A state of full mental investment is necessary to perform Knowledge work. To maintain that concentration we must ignore vision reflexes. But we can't stop 'subliminally seeing' threat movement and we can't tell our brain not to attempt a vision reflex. Psychology lectures in the 1990's explained that a conflict arose in the mind then built to mental break. The designers and psychologists had found a conflict of physiology related to the vision "startle reflex". They did not understand what they had discovered. It was only applied to designing the business office. They thought they were the first to cause these small mental breaks. But this problem has always been present anytime those special circumstances were created through human history. An incident aboard the Belgian Polar Expedition, 1898/99, had already happened. Jumping Frenchmen of Main had been discovered and evaluated, 1880. Cabin Fever, a sudden mental event where one cabin-mate violently attacks others, had been noted during the fur trapping period in the United States. Culture Bound Syndromes involving dissociation and psychotic episodes are the same mental events happening around the world. The phenomenon is so simple that it can be proposed as a cause of mental illness through history. Posted from VisionAndPsychosis.Net by the author. http://VisionAndPsychosis.Net