I do the same 15 second dash when I forget my keys.
It is my job to make it very difficult for bad things to happen to my son. I don't want to delegate that job to him, by teaching him fear. Upon a lot of reflection and talking to dw. I think we will wait till he is going out on his own (when ever that will be) before we have that talk.
Before then he can not help but pick up on my non verbal cues. I am sure he is aware that I am more nervous in some situations than other, and with some people. I try to give everyone the benefit of the doubt but ... when it comes down to it I'm still careful.