Dissociation is a coping strategy and a symptom that is often associated with complex trauma.
And EMDR is a therapy that can rapidly uncover this symptom given it was developed as a treatment for PTSD.
That is why if you know that you struggle with dissociation EMDR in the right hands can be powerfully effective and in the wrong hands it can be damaging.
If you think EMDR might be useful for you, I strongly recommend researching your therapist and finding out if they are certified in EMDR and if they have had training or supervision in working with dissociation. Those are two things that increase the chances of having a successful EMDR therapy experience.