He is I'm afraid to say entirely wrong! Dissociation is neither a choice nor a thing of the head. It is the bi-directionality of our underlying autonomic nervous system (specifically our ventral vagal complex that either adaptively and interoceptively "feels" embodied and safe with relationship to others and surrounding or if not "safe" then adaptively in a state of defensive fight/flight sympathetic-adrenal arousal or if fight/flight is not available then what we refer to as dorsal vagal shutdown (withdrawn and/or dissociated). However, often combinations of all the forgoing.