I know this post has been sitting here for a while, but it does not appear to have been answered and I just had to figure out the same issue.
Couldn't tell from the OP whether this question applies to VLC on Windows, but if it does, then...
- Select the VLC window (click somewhere within it to make it active or Alt-Tab to it.)
- Press Alt+Space to get to the context menu for the VLC window (or any other window for that matter).
- Press the "S" key to pick the "Size" option (at least on Win-7 and Win-XP it's "S") in the context menu.
- Press one of the scroll arrow keys to lock the sizing to one of the borders (up-arrow locks to the top border).
- Move the mouse around until you have the controls / menus back on the screen.
- Click a mouse button to release the lock on the window "Size" function.