Ah, Chris. It's as well you're a professional, isn't it.
What's missing from this? : sudo usermod -G somegroup, someothergroup, chris chris
Yes, that's right you missed out "sudoers" from the group list didn't you Chris, and we know what that means don't we Chris? Yes, that means you're removed from the group because you didn't include -a in the options. As yours is the only account in the sudoers group, and this server's root account is disabled, you're a bit f00ked now, aren't you Chris?
Fuckwit.
Recover Mode toooo the rescue!