When you hit CTRL+ALT+F1, you're going to see the "behind the scenes" starting of X. To get back to X from the command line, just hit ALT+F7.
F1-F6 are your virtual terminals. F7 and up would be your X sessions. It is possible to have multiple X sessions running at once, but I can't remember how it's done. There's a thread here about that though somewhere. Anyway, it sounds like all you need to do is hit your ALT+F7 to get back to where you were.
When you're not logged in, your X hasn't "officially" started. You're most likely under the spell of gdm or kdm at the GUI "login screen". So when you hit CTRL+ALT+F7, and you type
startx, it will start your X session. However, if you've already logged into X then go to virtual terminal 1 and type
startx, you'll get an error saying that you've already got a session open--at this point, ALT+F7 and you should be back in X. Let me know if this works out for you.