Apparently Ctrl+Alt+Fx keys on linux switch console sessions and #7 happens to be the main windowing session. So pressing this sends all your screen black and pauses all apps with no instructions. Which is pretty frightening really. Luckily you can get back by pressing Ctrl+Alt+F8. Hopefully you have a second computer or tablet/phone handy to find this blog post if that happens 🙂 BTW I’m using Linux Mint, YMMV with other distros.