Eye Movement Desensitization and Reprocessing (EMDR) therapy is an effective treatment for PTSD, anxiety, depression and eating disorders.
Often when something traumatic happens, it seems to get locked in the brain with the original picture, sounds, thoughts and feelings.
Since the experience is locked there, it continues to be triggered whenever a reminder comes up.
These are really the emotions connected with the old experience that are being triggered.
The eye movements used in EMDR seem to unlock the system and allow your brain to process the experience.
That may be what is happening in REM, or rapid eye movement sleep, when our most intense dreaming takes place.