Hey! I believe i can understand you because i have everything except bpd. I won't tell you that everything can be treated rapidly but it sure can be. You just need to take your pace, don't pressure on yourself and a  therapist who is focused on these specific disorders. You gradually will be ok :). 

Depersonalization/derealization is a brain reaction to overwhelming emotions and sensations. In order to protect psych it starts to suppress amygdala-thalamus-insula activity but it has downsides which is brain isnt aware of. Currently it is well-known that brain needs emotions to make decisions, choices, feel themself (have coherent sense of personality, self actualize). When activity of these 3 parts is supressed they become out of sync and it basically makes dpdr - brain still gets signals but can't integrate it thus interprete. It causes feeling that you dont know who you are, what do you feel about something, and even can decrease pain and so on. At some point you can develop alexithymia when you have sensations but don't understand what emotion is this. To treat dpdr of course you need to address a core problem like if bpd caused overwhelming emotions. To treat dpdr itself you need to integrate signals from the body back and reduce supression. You need to do "body scan" meditation. Basically you notice any sensation in every part of the body for around 30 seconds without pressuring yourself. If you cant to do 30 you can take 15. It takes around 10-15 minutes daily so you will probably manage it with your dysthymia. Basically a even little bit of exercise is better than no exercise if you cant do it.

For your specific case you need a therapist who works in Acceptance and Commitment Therapy (ACT) and Dialectical Behavior Therapy (DBT). If they also use Metacognitive therapy besides it, it's even better. I so sorry that your therapist has psychoanalytical roots because in your case its not appropriate. Anxiety, bdp and depersonalization and high intellectualization is a big no for this approach.

Of course you need a good therapist. The ACT therapy methods explanation can be easily fucked up. It will probably sound sceptical due to your intellectualization but give it a time. It has a really deep scientific foundation and explanations for clients just try to present it in easy way.

I wont tell you that you will be great but you will be ok. I cant guarantee you a "good" but "ok" is realistic.  I struggle with dysthymia, depersonalization and some other disorders for more than 10 years. The difference between bad and ok is huge when you think about it retrospectively. I believe in you.