There are several reasons that can contribute to failure, but they can be prevented and the time to try to "smooth".
The first reason is a strong psychological stress. To it are not everyday experiences, conflicts at home or at work, chronic fatigue and lack of sleep. This is usually a precarious situation: a divorce, a wedding, a funeral or something as emotionally rich.
The more common cause is physical stress to the body, which can cause as severe illness or surgery, and the disturbance of natural biorhythms.
In addition, significant strain the body is experiencing when he "planted" on a rigid diet or exhausting intense exercise. An extreme case is "teen anorexic", when even before the catastrophic decline in body mass observed cessation of menstruation.
In all these cases the reason for failure is a priority commitment of the organism to survive, while "pritormazhivayut" all other regulatory processes, and the main body are "thrown" on the removal of the body from the dangerous situation for him. Of course, it would be wise not to bring the body to such a state when he is forced to disable the processes which are "not a priority". But if you do, you need to gradually get out of the "extreme mode", revise and re-build the processes that led to the failure to adjust training schedule to consult with a nutritionist about the ideal weight, change jobs, and the mode of the day.
If the failure cause was emotional stress – there is a reason to engage auto-training, yoga, or work with a psychologist. Should not be disregarded, and "grandma's remedies" - motherwort and Valerian.
If cycle failures occur frequently, regardless of age, be sure to consult your doctor as it can indicate hormonal problems in the body.