Hi. I have a 2010 Prius. I usually get about 600 miles per tank, which is about a week's worth of driving. Now, I'm only getting about 200 miles per tank. I am filling up every other day. No lights are on on the dash and no messages pop up. The car has 84k miles on it. I change the oil regularly. Any thoughts? I'm afraid to bring it to the dealer to get diagnosed until I have some idea what is going on.