Very often there is no external cause for the breakdown.
It is because there is a lack of hormone - serotonin - that causes acute depression leading to the breakdown behaviour you describe.
Extremity is the key. Whilst one person may display hyperactivity, restlessness, quickness to anger another may be lethargic, slow to react and show no interest in the world around them.
Very often there is a tendency to hypochondria - feeling physically unwell with a wide range of symptoms that may not be real can be an indicator. This 'unwellness' will be used as an excuse to avoid situations.
Mild paranoia may also be present - a feeling of persecution, being watched.
It is incredibly difficult for the experts to diagnose - especially as the 'patient' may deliberately mislead the doctor as to his true behaviour and feelings.
Talk to your GP.