I looked in the mirror today to begin brushing my teeth and they were dark next to the gumline and part of one of my teeth was gone! I especially noticed this when I was flossing. My teeth, recently have been more sensitive than normal to cold only. Am I losing my teeth?! Are they decaying? This is not normal! They don't hurt, I feel normal, but have to chew anything a little less aggressively because it feels like it might hurt if I bite hard. What is wrong?! I do not have health insurance--my insurance stopped that part of the health coverage. Please help.