Did you try switching the ignition on to look at the temperature gauge? If the temp sensor is causing it, then it's probably telling the ECU that it's way too hot. Your gauge may reflect that.

Can you plug in a scan tool and see if there are any codes?

Cycling the ignition might also cause it to just stop doing that. Not like that's a good thing, because you'll never find out why it happened, but it might just resolve all on its own that way.

If that doesn't clear it up, maybe unplugging the battery for a bit?