Welcome. I relate to feeling like your nervous system has a life of its own. The nervous system can release old traumas, learn new patterns, change, and come closer to balance. In nerd terms this is simply the science of neuroplasticity. For me the hard, frustrating part is just feelin stuck sometimes because I don't know what to do exactly to re-wire or re-write an old pattern...or I feel good with the familiarity sometimes, especially in my more hyper states.
For me, these changes (or being stuck) are also in spite of my intelligence, like you mentioned. While a little research can be helpful sometimes, in the case of recovering my nervous system I think my need to know and understand actually holds me back sometimes...it's the part of me that drops into familiarity when I don't understand new information fast enough. I have to remain curious...willing to try new things, notice what I'm experiencing in my body, what helps, what doesn't, what is different, etc. But honestly, I'd believe it's not a quick process, even when we're really determined (patience is hard for me).
There's some abuse in my past but my extremely life-threatening traumas happened when I was very young and I don't believe I gained a very reliable sense of safety from my connection to my mom, since she was half terrifying. For most of my life I isolate to find safety, yet never really find it on my own....but also, there have been a lot of good moments, possibly as outcome of my fierce need to create meaning and good experiences. I've felt before that I am stuck in a pattern of over-drive and self-destruction that are so deepply part of who I am that I cannot change. But the extremes of energy out-put day to day have truly come closer to center over the past few years (I'm not stuck so much in extremes of hyper or frozen/paralyzed but operate more moderately active in my life...still tipping towards those ends when stressed or in pain, but it's much different and I'm not outright self-destructive....oddly I have an inner desire to take care of myself and I honestly believe that was absent for the first few decades of my life, so big changes CAN happen....gradually...)
I never thought it could be, but slowly I AM changing....and for me slow is key because I don't become entirely depersonalized in the process. It's harder to notice slow gradual change, but working steady and easy in therapy and day-to-day-life helps me remain intact....or I should say slowly pull the pieces of myself together vs fall apart. Even if they went missing before age 4, I do believe I can rewire my being to feel wholeness and safety. It's just taking time and commitment to my life.
Best wishes...that you are here suggests you still have hope. I hope this forum is helpful. Be kind to yourself one moment at a time.