The word "breakdown" is often used to describe the mental collapse of someone who has been under intolerable strain. There is usually an (inappropriate) inference of "mental illness". All these are lay terms and mean different things to different people. I define two types of breakdown:
Nervous breakdown or mental breakdown is a consequence of mental illness
Stress breakdown is a psychiatric injury, which is a normal reaction to an abnormal situation
The two types of breakdown are distinct and should not be confused. A stress breakdown is a natural and normal conclusion to a period of prolonged negative stress; the body is saying "I'm not designed to operate under these conditions of prolonged negative stress so I am going to do something dramatic to ensure that you reduce or eliminate the stress otherwise your body may suffer irreparable damage; you must take action now". A stress breakdown is often predictable days - sometimes weeks - in advance as the person's fear, fragility, obsessiveness, hypervigilance and hypersensitivity combine to evolve into paranoia (as evidenced by increasingly bizarre talk of conspiracy or MI6). If this happens, a stress breakdown is only days or even hours away and the person needs urgent medical help. The risk of suicide at this point is heightened.