In my own opinion, the most important thing is that the person is reasonably reputable (they should have actual credentials, lol...make sure they're a real therapist). But beyond that, just make sure you like them.
The 'fit" between patient/therapist is what will really cure or fail you. The actual work done in the treatment will be done by YOU - therapist is only a guide, and a highly imperfect one at that. If you can find someone you believe you will ULTIMATELY be able to trust, that's half the battle. And then, over time, slowly and cautiously you might be able to open up, and really talk about some stuff you've never let into your own conscious mind before. That's when Change can occur, and that's when symptoms can vanish. Ain't easy, ain't quick, and worse, ain't no guarantee. But if you can find someone you FIT well with, you increase your chances 10,000 fold.
Do they need to know dp? nope. Treatment is the same for anxiety, dp, depression, ocd, etc. Naturally, there are distinctions in the TYPES of patients who develop each symptom, and in that sense it CAN be useful sometimes for a doctor to be experienced with DP-TYPEs (the obsessive, the narcissstic, the highly controlled, the self-vigilant). But the actual experience of BEING dp'd is for you and you alone. Talk therapy works because of all the other stuff you'll explore in that room, not your symptoms.
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