The method is called hypnosis.
Catharsis (from Greek 'cleansing') is the purification and purgation of emotions that results in renewal and restoration. In psychology, the term was first employed by Josef Breuer who developed a cathartic treatment through the use of hypnosis. The aim of this treatment was to enable the hypnotized patient to recollect the traumatic events and to eliminate them through catharsis.
Under hypnosis, patients are able to remember long forgotten past traumatic events. The original emotions were recalled and expressed ( catharsis ) and the patients relieved of their symptoms.
Hypnosis is a state of human consciousness involving focused attention, reduced peripheral awareness, and an advanced capacity to respond to ideas and suggestions.