Slips into Neutral?

I have a 2008 Prius with about 95,000 miles. It is bloody cold here. About 4 degrees F when I got up. On the way to work, on the parkway, suddenly the car lost power entirely. Just started to slow down. No reaction when I pressed on the gas pedal. I didn't notice any warning lights. I flipped the gear shift to Drive, and the car accelerated again. About five minutes later, this repeated. For the rest of the trip it was fine, and there were no problems coming home. (Temperatures were still way below freezing in the afternoon when I left work though the car had been sitting in the sun. I don't know if this could be cold-related, but it's never happened before and it hasn't been this cold here for days on end before._