This was on TV yesterday. Captain Kirk was split in a transporter malfunction, between a "good" self and a "bad" self. Broadly, this was his intellectual or rational self, and his instinctive or animal self. One could not survive without the other.
"When humans begin to move out of the immobility response, we are often frightened by the intensity of our own energy and latent aggression, and we brace ourselves against the power of the sensations. This bracing prevents the complete discharge of energy necessary to restore normal functioning."
"Traumatised people generally have become fearful of their own aggression. When they begin to emerge from immobility, they suppress this life-saving aggressive response. This suppression has the consequence of throwing them back into paralysis. Thus, with their aggression thwarted, they remain fearful of re-engaging in life."
Peter Levine, Healing Trauma.