Just as a phantom limb is the sensation of the presence of a missing limb, phantom morph disorder is the feeling that you are in a different body. The mind expects sensations and feedback that is no longer being provided, resulting in disorientation, alienation and phantom sensations.
If the new body is similar to the old, phantom morph disorder is effectively impossible. If the morph is only somewhat different, the disorder is mild, and usually temporary. If the new body is very different, the disorder is at its worst, and is sometimes permanent. Victims can feel as if their old bodies are being forced into the shape of the new one, usually experienced as pain, a confused ability to control their morph, and a fearful dissociation from the morph. When Fall refugees who grew up in their birth bodies had to sleeve into spare octomorphs, they had to constantly fight against the conviction that their limbs had been split and their head moved into their torso.