yes, i have read that such things can come from surgery, injury, and/or hospitalization. in fact, i think one of my early ones did too. i was hospitalized for bhronchial asthma at 3 and turned into a "wild animal" when any dr or nurse came within 5 feet of my crib. i'd growl this highish growl just at the mere presence of them. i was "a complete monster" who refused to take medicines and physically fought off check ups. it took 3 nurses and a dr to hold me down - i imagine this could not have been good on the psyche. i haven't changed - as i grew up, any time i felt threatened like that i turned into this wild thing that would have to be restrained - it happened again medically when i was 8/9 for injections - again took 3 nurses to pin me down to the bed (face down) and wrench my arm backwards to give me the injection (this happened twice). so i guess then the egostate or alter confirmed that this is a useful thing and kept the ability to split off for these times. i've used it at least 5 times - twice fighting off family members trying to restrain me. I didn't think of this until now.
kiya