I've read before that you need to be careful.
I also found the below which might be useful -
Levels of Dissociation
The standard EMDR protocols only address the primary and secondary dissociation that frequently accompany and follow traumatic events. These two types of dissociative symptoms typically are symptoms of posttraumatic stress disorder. Primary dissociation consists of flashbacks, intrusive thoughts, and somatic symptoms. Secondary dissociation consists of depersonalization and derealization.
In contrast, tertiary dissociation, which is addressed by the proposed treatment model, includes the formation of a range of ego states, from normal functional parts to less functional self fragments or alters. Tertiary dissociation is considered ubiquitous. Bromberg (1994) and Watkins and Watkins (1996) describe the formation of ego states as a line of normal human development.
In the EMDR treatment of dissociated, traumatized clients who are dealing with these less functional parts, ego state work needs to be an essential part of the preparation stage. If it is not, as mentioned above, there may be diminished response or nonresponse to treatment.
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