The same thing had been happening a lot lately, but it should be back to normal in a few moments. There have been several threads discussing the same issue on the meta so far, maybe you'll want to take a look too and find some helpful answers.
Here's their response some time ago about the same issue:
My best guess at this point is that it was a random failure of some networking hardware. It doesn't look like any failure I've seen before, so it's difficult to diagnose. It doesn't particularly look like a DDoS or other attack, though I can't rule it out.
There won't be any downtime if/when I change anything regarding images.