I can understand your reaction to things like that. Not being startled during traumatic events was something I had developed as well. I often just take things in and process them and move on. Always thought I was a bit callous in that sense but I do believe it was my 'conditioning' to chaos.
There are times I do get jumpy but that is when things are calm. I am looking for the roof to cave in so to speak. I am getting better with enjoying the quiet times in my life but it has taken some practice.