I think the problems started around 3.5-4 hours ago, with some timeouts and general slowness.

Then the site was down for a couple of hours, and as commented (and I'm posting, so it must be true!), it's back up now although slow.

Hopefully will improve speed-wise soon, although my suspicion is that there was a database issue which has been resolved, but re-indexing is taking place (or something similar) and causing the ongoing issues.