What happened:
I shelled into the linux VM and started looking at logs etc. because it was refusing to relay mail. Suddenly I got a bunch of i/o error messages and couldn't find "yum" and crap like that. I looked at the console and it was filled with errors.
What I did:
Restarted the VM, it dumped me to a root shell with an error I was too stupid to write down or screenshot but it was related to corruption.
I booted the VM from a Centos ISO (after adjusting the boot delay to 10000 milliseconds so that I could enter the BIOS and select the CD-ROM as a boot device) and went into rescue mode. It said "you don't have any linux partitions" and dumped me to a shell.
Using http://jim-zimmerman.com/?p=587 as a reference, I ran lvm vgscan -v and discerned that my lvm group name was "cl" (presumably "centos linux"). I then did lvm vgchange -a y to "activate" all volume groups, whatever the hell THAT means. Now I could see and mount /dev/cl/home and /dev/cl/boot and see their data.
I then tried mount /dev/cl/root but it said "failed: Structure needs cleaning"
I then ran xfs_repair -L /dev/cl/root and it spewed a ton of output.
Afterward the VM booted fine. YAY