I have had similar dreams and I feel that it was my body's way of telling me not to eat certain foods. This was correct for me. How is your diet right now? Are there foods you're eating that you feel are actually 'making you sick'?
Or...maybe there is something inside you (it's dark in there, remember!) that needs to come out into the light of day so you can take a better look at it.
Black tar and white cloth? Interesting. Black and White (bad/good imperfect/perfect etc etc) - do you have judgement about the foods you eat? Or would you say you are a black and white kind of person?
There are lots of options with this dream...maybe one of the above things clicked...then you can simply follow the thread and see where it takes you!