When a human being is exposed to threat, networks of brain cells are activated so that person can act to protect themselves from harm .
This emergency response means that a human being will either overcome the threat or run away [fight or flight] , or freeze [ no visible response , so the threat goes away .]
If an emergency response was not possible in these ways or the threat did not go away , these networks are reactivated in the present each time there is a potential threat , direct or indirect [ e.g. watching threatening content on t.v. ] .This is why the trauma of the past is still experienced as if it is still happening now , causing distress.
A person may experience overwhelming reexperiencing of the trauma [flashbacks] , intrusive memories or negative beliefs about themselves , images and feelings or an absence of feeling .
An absence of feeling because of shut down causes distressing emotional numbness and lack of connection with self and others [Dissociation] . Overwhelming feelings can change abruptly and be experienced as mood swings or difficulty with emotional regulation . Intense feelings of fear, anger , anxiety and sadness are normal .
A common way to cope with this is to avoid potential threats [avoidance] , the result being that a person can become isolated . It is common for trauma to lie at the root of anxiety and depression and for the experience of mental illness to be a traumatising experience in itself.