Whenever you install or remove software, be sure to read through what’s being removed. You don’t want to accidentally uninstall something important. This is very unlikely to happen with official Debian packages, but you should be especially careful when installing packages outside of Debian’s repo, as they may not be fully compatible with your version of Debian.
In any case, I’d log in to a tty (ctrl-alt-any function key) and install whichever desktop environment you had before using apt.