I have been experiencing extreme dry mouth. My tongue was completely discolored. I have been scrubbing my tongue and the color is turning back to normal. When I rinse after brushing my spit is slimy. My taste is totally off. Nothing taste right. I am drinking mostly water and milk. These are the only two things that don't taste awful. I have been very tired and experiencing nausea. What would cause the tongue to be discolored? It has a white color and a dark color in the middle on the back of the tongue?