Edit: Dreamhost is AWESOME. Their reply got back to me within ten minutes:
Sorry about that. The server you are on needed to be rebooted due to
becoming unresponsive. The reboot appears to have fixed the issue. Our
administration team will keep an eye on the server to make sure that no
further issues continue. Due to the added problems you mentioned above I
have requested and tagged the server for a full evaluation.
Thanks!