Dissociation As a defense against emotional pain, dissociation is separation from and loss of awareness of our experience of the present moment.
Repression is similar and related to dissociation and denial. Repression is an automatic psychological defense against unbearable emotional pain wherein we forget a painful experience and store it in our unconscious mind.
Denial is complex defense that involves not recognizing and thus avoiding our awareness of the reality of a traumatic experience. While considered a "normal" defense at times because it may allow a graded acceptance of hurt, loss or trauma, denial is maladaptive if it interferes with rational or appropriate action to address or heal the hurt, loss or trauma...
( fromMemory and Abuse, remembering and healing the affects of trauma, by Charles L. Whitfield M.D. Health Communications Inc. 1993)