There have been a few issues with the Showdown server today. I got an alert from my host that the server that PS runs on had been running at very high CPU. It turned out to be something to do with NodeJS (the programming that PS uses). I restarted the server and the CPU went back to normal, but an hour later it went back up again.
I haven't found the exact cause of the issue. I don't know if it's something in Showdown itself or whether it was some kind of DDoS hitting the server. I opened an issue here on the Pokemon Showdown GitHub repo in case Zarel can shed any light.
I've restarted again and it seems OK at the moment but I may need to take the server down for a while if it doesn't get resolved. Just wanted to let everyone know.