I think it has to do with altered fight-or-flight response; I was never so over-sensitized like this until I reached a certain point with the type and number of trauma I eventually had to contend with. I'm now much less easily triggered by big events in the moment that most people would naturally be more triggered by, like a swerving car or other threatening situations, while against many little things I'm entirely helpless to defend myself. For me I think it was when my instinct to always be bracing myself for the potential of bigger trauma became second nature that as a result I became hypersensitive to things like noises or temperature changes or things touching my skin that ultimately shouldn't be that big of a deal. My body is bracing for the wrong things, making the whole system wonky.. thermoregulation and heart rate being especially out of whack for me.