Occasionally I put my screen session into a state that I call sulking – it refuses to take new input. This happens in two ways – one, my screen session gets fired into the background, and I left with the message [1]+ Stopped screen; the other seems to lock the screen from showing me any input. In the second state I can navigate among screen sessions, and create new instances, but not type.

After much thrashing about, I learned that when I hit C-a z (Control a, z) I put the session in the background, and it can be returned with the command fg. Similarly, if I hit C-a s I have locked the session to input, and to return it I need to hit C-a q. Good things to know.