The term nervous breakdown" is not a medical term and is not listed as a psychiatric disorder in any medical text. It is a publicly (non-medically) coined term used in common language and speech to indicate a highly stressed state of mind.

A person having a nervous breakdown may have been greatly depressed or anxious for a long period of time before the breakdown. In extreme cases of breakdown, people also lose their awareness of reality, which is also known as impaired reality testing. Day to day activities and chores are seen as impossible tasks by nervous wrecks.

Nervous breakdown in simpler terms is described as an acute attack of mental illness characterized by depression and anxiety. Once we are affected with mental breakdown then our morale goes down. The first thing we start with is lack self confidence. We start losing our energy and start wasting our time by pondering over stupid things. It is because our reasoning ability is heavily affected and we tend to misjudge things. Moreover the lack of motivation worsens the situation. Thus the control over us starts weakening.

Breakdowns involving psychosis
In extreme psychotic cases of breakdowns people may have visions and hallucinations, hear voices that are not present or feel vibrations and sensations which actually should not exist. Post partum psychosis involves a broken person being obsessed with thoughts of harming someone or troubling someone like one's own child or relative.

Breakdowns may also lead to a persecution syndrome, in which the sufferer will always feel that everybody around him is plotting to harm them which in actuality will not be the case. A person during a nervous crash might also be overloaded with emotions of generosity, jealously and guilt. The speech of such a person may become incomprehensible due to a strange presentation and organization of language. Body movements may become jerky and a mentally broken person might even contemplate perverse and bizarre actions like public nudity.

Breakdowns involving bi-polar (manic) behavior
People who have a history of bi-polar disorder experience insomnia coupled with elevated energy levels in a nervous breakdown. They display weak decision making capabilities and poor social judgment and behavior. For example a person might talk too much publicly or spend too much or have an overstated self-esteem.

Breakdowns involving Anxiety disorders
Breakdowns rooted in anxiety disorders are characterized by panic attacks and immense sensations of fear. The fear may be debilitating, drastically affecting the working and personal life of the person having the breakdown. A general feature of all nervous breakdowns is that the person starts moving away from a customary lifestyle towards a chaotic emotional turmoil that enhances the inhibition of day to day functioning.