My son-in-law is a lifetime member of the New York Athletic Club. He often takes me along on club fishing trips as a guest. The other members are very nice to me.
One time, they asked me how I slept last night. I didn't know what to say. On the side, I asked my son-in-law, "Why did they say that? Isn't that kind of personal?"
My son-in-law said it is a common American expression and they were just being friendly. In my sixty-something years in the United States, I had never heard that expression before. In China, no one ever asks someone how they slept!