Oh gosh no! Keep on brushing not only your teeth, but your tongue as well!
It is typical during a fast for your tongue to be coated in white and your breath can get very funky.
I notice that the more I cleanse the less this is true, but it did take me a LOT of fasting to finally get my tongue pink again!
Another weird thing. Smells are really sharp, both good and bad, while fasting. You can tell when someone's had garlic for lunch (two days ago) from 40 paces... and cooking dinner for your family takes on a whole new meaning! I sniff ALL that food! It smells WONDERFUL!