The tongue coating can also mean food alleriges or in chinese medicine it means dampness which can be an infection: fungal, bacterial,or viral. It can also indicate a toxic liver and digestion system.
I notice if i eat somehting I am allergic to it goes really thick and yucky. I also notice that when I am detoxing from fungal it goes really thick. When I use a good probiotic it goes nice and clear and also when I eat garlic.