Threw me for a loop

What is the meaning behind this saying?

Roughly "stunned me," in either a good or a bad sense. To knock or throw somebody for a loop originally meant to render the person unconscious or (in figurative use) "to make a strong, favorable impression on someone" (Wentworth & Flexner, "Dictionary of American Slang," 1960). "Loop" has been used to mean someone who is stupid or drunk or simply a nobody: "a person with nothing inside" (Dict. Amer. Slang).

Or simply turned me upside down, or 180 degrees from my original thinking.