How to get back to insert mode in VIM when you accidentally hit C-x C-s

Given this vim session:

% vim test-file.txt
iHello there!C-x C-s

How do I get back to insert/command mode again? (C-x C-s means Control-x Control-s, not sure if it's normal vi terminology for keyboard shortcuts)

I know there's some way to get out of this and into insert/command mode again, but I just can't remember how and searching Google or superuser hasn't yielded me anything.

This happens since I mostly use emacs, but I use vim for remote hosts where I don't have emacs installed. Occasionally I do this and I figured I should learn how to get out instead of just restarting the terminal every time.

C-q. in a console C-s is scroll lock, resume is C-q