Could you please tell me the meaning of "knocked down and out" in this excerpt from the chapter Nine of The Great Gatsby? What is the difference between "knocked down" / knocked out" and "knocked down and out"?
Dear Mr. Carraway. This has been one of the most terrible shocks of my life to me I hardly can believe it that it is true at all. Such a mad act as that man did should make us all think, I cannot come down now as I am tied up in some very important business and cannot get mixed up in this thing now. If there is anything I can do a little later let me know in a letter by Edgar. I hardly know where I am when I hear about a thing like this and am completely knocked down and out.