Ctrl-z will send Vim to the background (though you probably can't be in insert mode). `fg` in the shell will then bring the Vim session back to the foreground.

Ctrl-z will send Vim to the background (though you probably can't be in insert mode). `fg` in the shell will then bring the Vim session back to the foreground. If `:sh` doesn't give you your command history and the same working directory, that might be convenient.