OK, I was doing some debugging with Xorg, and thought I had to use the Magic SysRq key to kill it. But when I had pressed Alt-SysRq-R to give the keyboard control from Xorg back to the kernel, it turned out that I not longer needed to do another SysRq because my Xorg magically worked again… Unfortunately now, everytime I pressed Alt-F4 to close a window, I found myself on tty4… rather poor. So I needed some way to tell Xorg to grab the keyboard again, and there it is: Just open an xterm and execute

sudo kbd_mode -s