I've got an 08 with 139k on it. This happened to me yesterday & today. Luckily I found this post & check the oil. It was very low, like barely on the dipstick. I've got an oil change scheduled for Saturday morning. I put two quarts in it just now & it's a little less than midway between the two points on the dipstick. I'll be more careful about checking the oil. With my Prius getting on in age, I need to be more cautious about issues popping up.
Used to be a company that made an electronic dipstick (Intellistick) that sent level and temperature data via Bluetooth to your phone. Unfortunately they are out of business.
Dear friends, check your oil level regularly! Luckily I found this topic, my oil level was deep below dipstick!!! Added 1.5 litres of oil...