For me, I think that I have a highly sensitive nervous system. I get dysregulated easily, but I learned from an early age (basically birth; I have attachment trauma) that it's safer to push down the symptoms of dysregulation. I'm also in my late 30s and even though I've had SI symptoms since age ~8, I only became completely unable to function when I was 36. For me, it was like I was overdrafting my bank account for 30+ years and then one day, I just couldn't anymore.
Another piece that I've thought about is the role of temperament. My parents complained incessantly about how much I cried as a baby and how my sleep cycle was reversed for a long time (I slept all day and would be up crying all night). My guess (no evidence) is that my temperament was very different than my caregivers as a baby and that disrupted my nervous system very early on.
Another, the final, piece is that my siblings have their own issues that affected me. My older sister has undiagnosed BPD and my younger sister was neglected as in infant, which led to a ton of development disabilities for her. I was born between my 2 siblings... so, I have an older sibling who could not regulate her own emotions and had (scary to me) emotional outbursts, and a younger sibling who was significantly developmentally impaired (as children I often stood up to her bullies and tried to protect my younger sister). I believe that in my personal life situation I didn't have much of a chance of doing well as an adult!
Hope you're okay. <3
