Has an 18 wheeler ever scared the crap out of you?

I used to have a little old Vega when I was a teenager. There is a portion of the highway leading out of the city where you have to do a lot of lane changing to either make way for people on-coming, or to take the last exit, or to move in to the the toll road lane. (It’s really quite a mess and not well thought-out.)
During all this maneuvering an 18 wheeler ended up behind me. He was so close that ALL I could see was his grill completely filling the back window when I looked in my rear view mirror. It was terrifying and mesmerizing at the same time.