Vim crashing when pressing `ctrl-s` in terminal
See these questions and their accompanying answers on unix.stackexchange:
Ctrl+s hang terminal emulator?
How to unfreeze after accidentally pressing Ctrl+S in a terminal?
In short, Vim's fine1, it's your terminal pausing for, as usual, historical reasons. Press Ctrl-q to resume.
1) Okay, Vim might not be fine after SIGKILLing it, but the Ctrl+s didn't hurt it.