Waking up with putrid aftertaste in mouth? Possible Problems?

I was wondering what could be going on? When I wake up, I will have a very unpleasant taste in my mouth, kind of like drinking too much coke feeling. However, I did not drink any coke as have been aseep for 8 hours. This has been going on for a few weeks. What the heck could this be? It is similiar to cottonmouth or dry mouth.