This is obviously a stupid question. I am coding in Eclipse both on Mac and Linux, but I mixed up and used the Mac shortcut to window tabbing (Ctrl-Cmd-F6), but I was using the Linux on uni and screen went black. I've done this before, but this time I can't get back to my desktop. Ctrl-Alt F1-F6 gives me different terminals, F7 gives me a black screen and F8 a blinking underscore in the top left corner. Shouldn't my session have been somewhere in F1-F6 and is it lost?
X is probably still running on F7, your display driver (or something else) is just misbehaving. You might be able to trick it into coming back on by going to F7 and blindly opening a terminal and playing with xset ($ xset dpms force on). Or you can ctrl-alt-backspace to kill X and GDM should restart it.
Try seeing if you can repeat the problem and then file a bug report (or let the lab admin know if it isn't your computer). It probably has something to do with your distro's kernel configuration/patching. I've had this happen before on Ubuntu but not any other distros (I've used many), which is why I am assuming it might be distro-specific issue. Probably the unintended consequences of some kernel patching.