Reading your experience through my personal lens:
This sounds like an emotional would. People don't close up and shut down unless they've been deeply hurt. I'm just starting to heal from my neglectful childhood, and I experience much of the same. It's hard to feel, it's hard to sit still (because that's when the bad feelings return, also ADHD), and it's nigh impossible to let people in.
Thank you for opening up in this thread, seriously. Thank you for being a little bit vulnerable.
I can't say if you're neurodivergent, or have "just" gone through some shit. I can say that neurodivergent people are often the target of abuse and neglect.
I'd like to add that a common symptom of burnout is the exhaustion of empathy. When you no longer have the energy to care for yourself, you cannot care much about other people either.
Take care of yourself, comrade. <3