[IAmGraydon]

Derealization/depersonalization (known as DPDR) is a defense mechanism against painful sensory input - typically fear and/or anxiety. You brain sort of attenuates the external world and goes inside itself like a turtle that thinks it’s in danger. The state normally occurs in response to dangerous or traumatic situations (you often hear about out of body experiences in these situations), but particularly traumatic experiences (often from hallucinogens, abuse, war, etc) can cause a sort of sensitization that makes DPDR chronic.