I’m using split panes in tmux – one being vim, the other being a shell. Sometimes, around once a day, vim freezes. I can move between panes, perform any tmux commands, just vim doesn’t react to anything. This happens only with tmux. My only solution for now is to kill that pane and create a new one.
You might have hit Ctrl+S, which turns off flow control in terminals and stops the terminal from accepting input. It is reenabled by pressing Ctrl+Q.
For me, this turned out to be a gpm problem. Run:
sudo service gym restart
See here for the related bug.