I seem to recall Percy asking for a report when this happens... I saw incredibly slow loading, several minutes per page, staring at around 7:50 AM Eastern and continuing for 20 minutes or so. I'm using a VPN for privacy and my IP starts with 209.222.
This has been going on for a while. I once tracked it down to many requests per second from an IP address. I blocked that address, but it happened again at a later date from a different IP. So I blocked that one instead, and then later it happened again from still a different IP. I eventually stopped trying to keep up with it. Every now and then some IP bangs on us really hard, and then everything slows down.
At one point last year it was so bad that it qualified as a genuine DOS (Denial of Service) attack, and our webhosting company shut us down because it was interfering with their own operations. I complained, to no avail. Apparently the Internet is still the wild west in some ways.