"Please don't imply that I should have known how to take care of myself"

No such implication was intended... I suggest self-defence classes now as a way to help you feel better about yourself now... and to help you get through that fear...

"I was taught that people seldom get attacked from behind"
Then you were taught poorly... A good teach would have told you that an attack can come from anywhere...

"my saving grace was sheer luck."
A good friend of mine says, "I'd rather be lucky than good", but another says, "I'd never trade skill for luck" heh