Spotlight search bar doesn't show up in middle of screen
The Spotlight window remembers its last location. You can drag it back to the original location — it snaps to the X and Y coordinates of the initial position, so you can ensure it is back where it started.

If the Spotlight bar does not remember its last location, make sure ~/Library/Preferences/com.apple.Spotlight.plist is writeable, as this plist file is where the coordinates are stored.